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

Abstract

The present invention provides a water-based ink composition for ballpoint pens that suppresses writing resistance at the tip of the pen, allowing for smooth writing even with writing instruments equipped with small-diameter balls, and that produces good handwriting without writing defects, as well as a ballpoint pen containing this ink composition. [Solution] An aqueous ink composition for ballpoint pens comprising a coloring agent, an alkenyl succinate, and water. The alkenyl succinate is dipotassium alkenyl succinate, and the content of the alkenyl succinate relative to the total mass of the ink composition is in the range of 0.2 to 5% by mass.

Description

[Technical Field]

[0001] The present invention relates to an aqueous ink composition for ballpoint pens and a ballpoint pen containing the same. [Background technology]

[0002] Conventionally, water-based inks (water-based inks) have been widely used due to their low odor and high safety. However, water-based inks have poorer lubricity than inks with organic solvents as the main solvent (oil-based inks), which can impair the writing feel and cause writing defects such as skipping or uneven writing. Therefore, it has been proposed to impart excellent lubricity to ink compositions by using polyglycerin isostearate ester as a shear viscosity reducing agent (see, for example, Patent Document 1). However, when the colorant content in the ink composition is high, the lubricity may become insufficient, indicating room for improvement in terms of lubricity. Furthermore, a writing instrument (reversible thermochromic ballpoint pen) has been proposed that contains a reversible thermochromic aqueous ink composition capable of forming handwriting that can alternately retain the state before and after discoloration in a certain temperature range such as room temperature (see, for example, Patent Document 2). This writing instrument contains a reversible thermochromic microcapsule pigment as a coloring agent in the ink composition. Because the reversible thermochromic microcapsule pigment contains a reversible thermochromic composition, which is the coloring agent, within microcapsules, the average particle size is larger than that of general-purpose pigments. Therefore, when an ink composition containing a reversible thermochromic microcapsule pigment is applied to a ballpoint pen, the rotation of the ball at the ballpoint pen tip is sometimes hindered, impairing the writing experience. The ink composition disclosed in Patent Document 1 allows the application of pigments as colorants. However, because reversible thermochromic microcapsule pigments are relatively special compared to general colorants, it has been difficult to achieve sufficient lubricity even when polyglycerin isostearate ester is used in the reversible thermochromic ink composition. In particular, when applying the reversible thermochromic aqueous ink composition to a ballpoint pen equipped with a small diameter ball, even greater lubricity is required, and there was room for improvement in terms of lubricity. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 1999 / 6494 Pamphlet [Patent Document 2] Japanese Patent Application Publication No. 7-186588 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention is based on the aforementioned background art and aims to provide a water-based ink composition for ballpoint pens that enables smooth writing even with a small-diameter ball (ballpoint pen) and produces good handwriting without writing defects, as well as a ballpoint pen containing this ink composition. [Means for solving the problem]

[0005] To solve the above problems, the present invention provides the following embodiments. [1] A water-based ink composition for ballpoint pens comprising a coloring agent, an alkenyl succinate, and water. [2] The ink composition of [1] wherein the alkenyl succinate is dipotassium alkenylsuccinate. [3] The ink composition according to [1] or [2], wherein the content of the alkenyl succinate relative to the total mass of the ink composition is in the range of 0.2 to 5% by mass. [4] An ink composition according to any of [1] to [3], wherein the coloring agent is a pigment. [5] The ink composition of [4] comprises 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 that determines the temperature at which the color reaction of components (a) and (b) occurs. [6] A ballpoint pen containing one of the ink compositions [1] to [5]. [7] A refill containing one of the ink compositions [1] to [5]. [8] A ballpoint pen [6] wherein the diameter of the ball provided at the writing tip of the ballpoint pen is 0.3 to 0.5 mm. [9] The refill of [7], wherein the diameter of the ball provided at the writing tip of the refill is 0.3 to 0.5 mm. [Effects of the Invention]

[0006] The present invention provides a water-based ink composition for ballpoint pens that, even with writing instruments (ballpoint pens) equipped with small-diameter balls, suppresses writing resistance at the tip of the pen, allowing for smooth writing and the formation of good handwriting without writing defects, and a ballpoint pen containing this ink composition. [Brief explanation of the drawing]

[0007] [Figure 1] This graph illustrates the hysteresis characteristics in the color density-temperature curve of a reversible thermochromic composition that decolorizes upon heating. [Figure 2] This graph illustrates the hysteresis characteristics in the color density-temperature curve of a reversible thermochromic composition that has color memory properties and heat-decolorizing properties. [Figure 3] It is a graph explaining the hysteresis characteristics in the color density - temperature curve of a heat - coloring type reversible thermochromic composition.

Embodiments for Carrying Out the Invention

[0008] [Aqueous Ink Composition for Ball Pens] The aqueous ink composition for ball pens according to the present invention (hereinafter sometimes referred to as "ink composition" or "ink") comprises a colorant, an alkenyl succinate, and water. Hereinafter, each component constituting the ink composition according to the present invention will be described.

[0009] [Colorant] 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 any one or more 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, mordant dyes, disperse dyes, etc. Examples of pigments include inorganic pigments, organic pigments, lustrous pigments, fluorescent pigments, phosphorescent pigments, etc. Further, water - dispersed pigments in which pigments are finely and stably dispersed in an aqueous medium using at least one of a surfactant and a resin in advance can also be used.

[0011] Also, a pigment dispersant can be used as needed. Examples of the pigment dispersant include surfactants such as anionic and non - ionic surfactants; anionic polymers such as polyacrylic acid and styrene - acrylic acid; non - ionic polymers such as PVP and PVA.

[0012] The pigments according to the present invention include self - dispersing pigments. Self-dispersing pigments are pigments that can be dispersed in an aqueous medium without the use of dispersants such as resins or surfactants. By subjecting the pigment to physical or chemical treatment to form hydrophilic functional groups on its surface, it becomes possible to disperse the pigment in an aqueous medium without the use of dispersants. Applicable pigments 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 contain encapsulated materials within a wall film formed by a wall-forming material. By encapsulating the encapsulated materials in microcapsules, they are isolated and protected from the external environment, thereby improving their water resistance and light resistance.

[0014] Examples of inclusions include colored compositions comprising a coloring material and a medium. Examples of colored compositions include those in which a dye or pigment as a coloring material is dissolved or dispersed in an aqueous or oily medium. The dyes or pigments described above may be used.

[0015] Examples of aqueous media include tap water, deionized water, ultrafiltered water, and distilled water. Examples of oily media include monobasic acid esters, dibasic acid monoesters, dibasic acid diesters, esters such as partial or complete esters of polyhydric alcohols, aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes, higher alcohols, ketones, and ethers. Aqueous media or oil-based media can be used individually or in combination of two or more.

[0016] As a 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. Examples of photochromic materials used as coloring compositions include coloring compositions in which a photochromic compound as a coloring material is dissolved in an oligomer as a medium, i.e., reversible photochromic compositions consisting of at least a photochromic compound and an oligomer. By encapsulating the reversible photochromic composition in microcapsules, reversible photochromic microcapsule pigments can be formed.

[0017] Examples of photochromic compounds include conventionally known spirooxazine derivatives, spiropyran derivatives, naphthopyran derivatives, etc., which develop color when irradiated with sunlight, ultraviolet light, or violet or blue light with a peak emission wavelength in the range of 400 to 495 nm, and lose their color when irradiation is stopped. Examples include the compounds described in Japanese Patent Publication No. 2021-120493 and International Publication No. 2020 / 137469. Furthermore, photochromic compounds having optical memory properties (color memory photochromic properties) can also be used. Examples of such photochromic compounds include diarylethene derivatives, and for example, the compound described in Japanese Patent Application Publication No. 2021-120493 can be cited.

[0018] Examples of oligomers include styrene-based oligomers, acrylic-based oligomers, terpene-based oligomers, and terpene-phenol-based oligomers. By dissolving photochromic compounds in various oligomers, both lightfastness and color intensity can be improved, and the sensitivity to color change can also be adjusted. Oligomers can be used individually or in combination of two or more types.

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

[0020] (Reversible thermochromic microcapsule pigment) The reversible thermochromic microcapsule pigment according to the present invention comprises a wall film and an encapsulated substance (including a reversible thermochromic composition described later) contained within the wall film.

[0021] ·Wall membrane The membrane forms an internal space in which the encapsulated material is contained, and this internal space is separated from the outside. As a result, the reversible thermochromic microcapsule pigment is less susceptible to external influences and protects the encapsulated material from various degradation factors.

[0022] The material that forms the wall film (hereinafter sometimes referred to as "wall film forming material") is not particularly limited. Examples include polyurea, polyamide, polyurethane, epoxy resin, melamine resin, urea resin, urea urethane resin, isocyanate resin, vinyl resin, gelatin, ethylcellulose, polyvinyl alcohol, carboxymethylcellulose, etc. These can be used individually or in combination of two or more.

[0023] • Inclusions Reversible thermochromic microcapsule pigments contain a reversible thermochromic composition as an encapsulation. The reversible thermochromic composition comprises at least (a) an electron-donating chromogenic organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of components (a) and (b) occurs.

[0024] The reversible thermochromic composition may be a heat-decolorizing type reversible thermochromic composition having a relatively small hysteresis width (ΔH) (ΔH = 1 to 7°C), as described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc. Heat-decolorizing type means that it decolorizes when heated and develops color when cooled. This reversible thermochromic composition changes color before and after a predetermined temperature (color change point), exhibiting a decolorized state in the temperature range above the high-temperature color change point and a colored state in the temperature range below the low-temperature color change point. Of the two states, only one specific state exists in the room temperature range, and the other state is maintained as long as the heat or cold required to bring about that state is applied, but returns to the state exhibited in the room temperature range when the application of heat or cold is stopped (see Figure 1).

[0025] The reversible thermochromic composition may be a heat-decolorizing type reversible thermochromic composition having a large hysteresis width (ΔH = 8 to 80°C) as described in Japanese Patent Publication No. 4-17154, Japanese Patent Application Publication No. 7-179777, Japanese Patent Application Publication No. 7-33997, Japanese Patent Application Publication No. 8-39936, Japanese Patent Application Publication No. 2005-1369, etc. Heat-decolorizing type means that it decolorizes when heated and develops color when cooled. This reversible thermochromic composition exhibits color memory properties in a specific temperature range (between the color development start temperature t2 and the color decolorization start temperature t3 (essentially a two-phase retention temperature range)). The shape of the curve plotting the change in color intensity due to temperature changes follows a significantly different path depending on whether the temperature is raised from a temperature below the color development temperature range or from a temperature above the color development temperature range t4. The colored state at temperatures below the complete color development temperature t1, or the decolorized state at high temperatures above the complete decolorization temperature t4, is determined to be color-memory (see Figure 2).

[0026] When applying the above-described reversible thermochromic composition having color memory properties, the reversible thermochromic composition can be specifically configured such that the complete color development temperature t1 is a temperature that can only be obtained in a freezer or cold region, and the complete decolorization temperature t4 is a temperature range that can be obtained from frictional heat from a friction body or a familiar heating element such as a hair dryer, and the ΔH value is specified to be 40 to 100°C, thereby effectively maintaining the color exhibited under normal conditions (daily living temperature range). Temperatures that can only be obtained in a freezer or cold region are in the range of -50 to 0°C, preferably -40 to -5°C, and more preferably -30 to -10°C. The temperature obtained from readily available heating elements such as hair dryers is 50 to 95°C, preferably in the range of 50 to 90°C, and more preferably in the range of 60 to 80°C.

[0027] The reversible thermochromic composition may be a heat-activated, reversible thermochromic composition using gallic acid ester, as described in Japanese Patent Publication No. 51-44706, Japanese Patent Application Publication No. 2003-253149, etc. Heat-activated means that it develops color when heated and disappears when cooled (see Figure 3).

[0028] The reversible thermochromic composition is a compatible mixture comprising the above-mentioned components (a), (b), and (c) as essential components. The proportion of each component depends on the concentration, discoloration temperature, discoloration form, or type of each component. Generally, the component ratio that yields the desired properties is in the range of 0.1 to 50 parts by mass, preferably 0.5 to 20 parts by mass, of component (b) per 1 part by mass of component (a), and 1 to 800 parts by mass, preferably 5 to 200 parts by mass, more preferably 5 to 100 parts by mass, and even more preferably 10 to 100 parts by mass of component (c).

[0029] ·others The reversible thermochromic microcapsule pigment may contain other components besides the aforementioned reversible thermochromic composition, as long as they do not affect its function. Other components include, for example, various additives such as antioxidants, ultraviolet absorbers, infrared absorbers, solubilizers, preservatives, and fungicides.

[0030] Reversible thermochromic microcapsule pigments or reversible photochromic microcapsule pigments may be blended with non-thermochromic colorants such as dyes or pigments. As a result, the reversible thermochromic microcapsule pigments or reversible photochromic microcapsule pigments change color from a first color to a second color.

[0031] Microencapsulated pigments are obtained by known microencapsulation methods. Examples of microencapsulation methods include interfacial polymerization, in situ polymerization, liquid curing and coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension and coating, and spray drying, and are selected as appropriate depending on the application.

[0032] Depending on the purpose, a resin coating or the like may be applied to the surface of the microcapsules to provide durability or modify the surface properties.

[0033] The microcapsule pigment preferably has a mass ratio of encapsulated material to wall film of 7:1 to 1:1. Having the mass ratio of encapsulated material to wall film within this range prevents a decrease in color density and vividness during color development. More preferably, the mass ratio of encapsulated material to wall film is 6:1 to 1:1.

[0034] Examples of resin particles include resin particles containing at least one of the above-mentioned dyes, pigments, thermochromic materials, and photochromic materials.

[0035] Examples of resin particles containing dyes include colored resin particles in which the dye is homogeneously dissolved or dispersed within the resin particles, and colored resin particles in which the dye is deposited onto the resin particles.

[0036] Examples of resin particles containing pigments include colored resin particles in which the pigment is homogeneously dispersed within the resin particles, and colored resin particles in which the surface of the resin particles is coated with pigment. Here, the pigment may be surface-treated by various conventionally known methods for the purpose of improving its dispersibility and adsorption to the resin constituting the resin particles.

[0037] Examples of resin particles containing a thermochromic material or a photochromic material include colored resin particles in which a reversible thermochromic composition or a reversible photochromic composition is homogeneously dispersed within the resin particles (hereinafter sometimes referred to as "reversible thermochromic resin particles" or "reversible photochromic resin particles"), and colored resin particles in which a reversible thermochromic composition or a reversible photochromic composition is homogeneously dispersed within the resin particles (hereinafter sometimes referred to as "reversible thermochromic resin particles" or "reversible photochromic resin particles").

[0038] The resin constituting the resin particles is not particularly limited as long as it is a thermoplastic resin or thermosetting resin, for example, 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, acrylonitrile-butadiene copolymer resin, etc. Thermosetting resins such as epoxy resins, epoxy acrylate resins, xylene resins, toluene resins, guanamine resins, benzoguanamine resins, melamine resins, urethane resins, phenolic resins, alkyd resins, polyamides, polyimides, polyamide esters, urea resins, silicone resins, and unsaturated polyesters. Each of these can be illustrated with an example.

[0039] The resin particles according to the present invention include solid resin particles with no voids inside the particle, and hollow resin particles with voids inside the particle.

[0040] Resin particles can be produced by pulverization, spray drying, or polymerization in which a dye, pigment, thermochromic material, and photochromic material are polymerized in an aqueous or oily medium. Examples of polymerization methods include suspension polymerization, suspension polycondensation, dispersion polymerization, and emulsion polymerization.

[0041] The shape of the resin particles is not particularly limited; spherical, ellipsoidal, or nearly spherical, polygonal, or flattened resin particles can be used. Among these, spherical resin particles are preferred.

[0042] Reversible thermochromic resin particles or reversible photochromic resin particles can also be made into resin particles that exhibit a color change behavior from a first color to a second color by incorporating non-coloring colorants such as general dyes or pigments into the resin particles.

[0043] The coloring agents according to the present invention can be used individually or in combination of two or more.

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

[0045] When the colorant is a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule 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 not particularly limited. Preferably, it is in the range of 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 ejection performance of the ballpoint pen containing the ink composition will decrease, and writing defects such as skipping or uneven lines will be more likely to occur. On the other hand, if the content is less than 5% by mass, it will be difficult to obtain suitable color change and line density for a ballpoint pen, and it will be difficult to fully satisfy the color change function.

[0046] When the colorant is a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, the average particle size of these colorants is not particularly limited. Preferably, it is 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 exceeds 5 μm, it becomes difficult to obtain good ink ejection performance 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 exhibit high-concentration color development.

[0047] The average particle diameter is the equivalent diameter of an isovolume sphere measured using a laser diffraction / scattering particle size distribution analyzer that has undergone a predetermined calibration [for example, Horiba, Ltd., product name: LA-960V2]. The average particle size is the average value of the equivalent diameter of an equal-volume sphere (the particle size D50, i.e., the median diameter, which corresponds to a frequency of 50% when the particle size distribution is determined based on volume).

[0048] The prescribed calibration will be explained. If the particle size of all microcapsules exceeds 0.20 μm, the average value of the equivalent diameter of equivolute spheres is measured using the Coulter method with a particle size distribution analyzer (e.g., Multisizer 4e, manufactured by Beckman Coulter, Inc.), and calibration is performed based on that value.

[0049] In cases other than those described above, the microcapsule region is determined using image analysis-based particle size distribution measurement software (for example, MacView, manufactured by Mountec Co., Ltd.), the projected area equivalent diameter (Heywood diameter) is calculated from the area of ​​the microcapsule region, and calibration is performed based on the average value of the equivalent diameter of an isovolume sphere calculated from that value.

[0050] <Alkenyl succinate> The ink composition according to the present invention contains an alkenyl succinate. The alkenyl succinate has the effect of suppressing the precipitation and / or aggregation of the colorant. This suppresses the obstruction of ball rotation in the ballpoint pen tip, reducing writing resistance and resulting in an ink composition that provides a smooth writing experience. In addition, the ink composition containing the colorant is more easily dispensed from the tip of the pen, resulting in a writing line with no writing defects and excellent density.

[0051] Alkenyl succinates are anionic surfactants represented by the following formula (I). [ka] (In the formula, R is an alkenyl group, X1 is a hydrogen atom or an alkali metal. X2 is a hydrogen atom or an alkali metal. However, at least one of X1 and X2 is an alkali metal.

[0052] The number of carbon atoms in the alkenyl group is preferably 8 to 22, more preferably 10 to 20. The alkenyl succinates according to the present invention can be used individually or in combination of two or more. The alkenyl succinates may be a mixture of alkenyl succinates with different numbers of carbon atoms in the alkenyl group, for example, C 16 ~C 18 Alkenyl succinates can be given as an example.

[0053] Examples of alkali metals include sodium or potassium. Potassium is preferred.

[0054] The alkenyl succinate according to the present invention may be a monosalt in which at least one of X1 and X2 is an alkali metal, or it may be a disalt in which both X1 and X2 are alkali metals. Preferably, it is an alkenyl succinate disalt.

[0055] Because it has an excellent effect in suppressing the precipitation and / or aggregation of colorants, the alkenyl succinate salt according to the present invention is more preferably a dipotassium alkenyl succinate salt in which both X1 and X2 are potassium, C 16 ~C 18 Dipotassium alkenylsuccinate salts are even more preferred.

[0056] The content of alkenyl succinate relative to the total mass of the ink composition is not particularly limited. Preferably, it is in the range of 0.2 to 5% by mass, more preferably 0.5 to 3% by mass. By having a content within the above range, it becomes easier to effectively exhibit the effect of suppressing writing resistance by alkenyl succinate.

[0057] Alkenyl succinates are anionic surfactants, and when the ink composition according to the present invention uses a pigment as a coloring agent, they adsorb to the surface of the pigment and function as a dispersant for the pigment. Therefore, even when the pigment content in the ink composition is high, the aggregation of the pigment is further suppressed, reducing writing resistance and providing a smooth writing feel. For this reason, it is preferable that the coloring agent in the ink composition according to the present invention is a pigment. Furthermore, when using reversible thermochromic microcapsule pigments as a coloring agent, the reversible thermochromic composition, which is the coloring agent, is encapsulated in microcapsules. As a result, the density of handwriting formed by a writing instrument using an ink composition containing reversible thermochromic microcapsule pigments tends to be lower than that of handwriting formed by a writing instrument using a general coloring agent. While it is conceivable to increase the content of reversible thermochromic microcapsule pigments to increase the density of the handwriting, increasing the content tends to cause aggregation of the reversible thermochromic microcapsule pigments, reducing lubricity. However, the ink composition according to the present invention is excellent at suppressing the aggregation of reversible thermochromic microcapsule pigments, reducing writing resistance and providing a smooth writing experience. Therefore, it is also preferable for the ink composition according to the present invention to contain reversible thermochromic microcapsule pigments as the coloring agent (pigment).

[0058] <Water> The ink composition according to the present invention further comprises water. There are no particular restrictions on the type of water used; for example, tap water, deionized water, ultrafiltered water, distilled water, etc., are examples. The water content relative to the total mass of the ink composition is not particularly limited. Preferably, it is in the range of 30 to 90% by mass, and more preferably 40 to 85% by mass.

[0059] <Thickening agent> The ink composition according to the present invention may further contain a thickening agent. By incorporating a thickening agent, it becomes easier to suppress the precipitation, aggregation, and / or sedimentation of the colorant. The thickening agent may be used alone or in combination of two or more types.

[0060] When the ink composition according to the present invention contains a thickening agent, the content of the thickening agent relative to the total mass of the ink composition is not particularly limited. Preferably, it is in the range of 0.1 to 20% by mass. By having the content within the above range, it becomes easy to achieve both good ink discharge during writing and the effect of suppressing the precipitation, aggregation, and / or sedimentation of the colorant.

[0061] While conventionally known thickeners can be used, it is preferable to use a substance that can impart shear viscosity reduction to the ink composition (shear viscosity reduction agent). Furthermore, the shear viscosity reduction of ink refers to the rheological property where, in a static state or under low stress, it has high viscosity and is difficult to flow, but as stress increases, its viscosity decreases and it becomes fluid. This property is also known as thixotropy or pseudoplasticity. Such ink compositions with shear-reducing viscosity are generally called gel inks and are used in writing instruments (ballpoint pens) equipped with a ballpoint pen tip. When gel ink is at rest and no shear stress is applied, it has high viscosity and is stably held within the ballpoint pen. During writing, the high shear stress generated by the high-speed rotation of the ball causes the ink near the ball to become less viscous, and as a result the ink is dispensed from the gap between the ball and the ball housing and adheres to the writing surface. Furthermore, gel ink can suppress the precipitation, aggregation, and / or sedimentation of colorants, as well as the bleeding of writing, thus enabling the formation of good writing. In addition, a ballpoint pen containing gel ink prevents ink leakage from the gap between the ball and the tip when not writing, and prevents ink separation and backflow when the writing tip is left upright. When writing, it is easy to ensure good ink discharge stability from the pen tip.

[0062] Examples of shear-thickening agents include water-soluble polysaccharides, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, poly-N-vinyl carboxylic acid amide crosslinks, 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 salts or amine salts of dialkyl sulfosuccinate.

[0063] Examples of water-soluble polysaccharides include xanthan gum, gellan gum, zeta-C gum, dieutan gum, macrophopsis gum, succinoglycans (for example, succinoglycans whose constituent monosaccharides are organic acid-modified heteropolysaccharides of glucose and galactose (average molecular weight of approximately 1 million to 8 million)), guar gum, locust bean gum and its derivatives, alkyl alginates, glucomannan, agar, and gelling carbohydrates extracted from seaweed such as carrageenan. Among these, xanthan gum or succinoglycan is preferred because it has excellent effect in providing shear-reducing viscosity.

[0064] Shear viscosity reducing agents are used individually or in combination of two or more types.

[0065] The content of the shear viscosity reducing agent relative to the total mass of the ink composition is not particularly limited. Preferably, it is in the range of 0.01 to 1% by mass, more preferably 0.05 to 0.5% by mass, and even more preferably 0.1 to 0.5% by mass.

[0066] <Other> The ink composition may also contain various additives as needed. Examples of additives include water-soluble organic solvents, water-soluble resins, specific gravity adjusters, surfactants, pH adjusters, resin particles, rust inhibitors, wetting agents, viscosity modifiers, preservatives or antifungal agents, foam absorbers, defoamers, antioxidants, and UV absorbers. These additives can be selected from those conventionally used in water-based inks and used as appropriate.

[0067] The ink composition according to the present invention can be manufactured by any conventionally known method. Specifically, the ink composition can be manufactured by mixing the required amounts of each of the above components and stirring them with various stirrers such as propeller stirrers, homodispersers, or homomixers, or by dispersing them with various dispersers such as bead mills.

[0068] The ink composition according to the present invention contains an alkenyl succinate, which suppresses writing resistance at the tip of the pen. This results in an ink composition that provides a smooth writing experience. The writing resistance of an ink composition can be evaluated by the difference between the average writing resistance value F1(g) of the ink composition according to the present invention (i.e., an ink composition containing alkenyl succinate) and the average writing resistance value F2(g) of an ink composition that does not contain alkenyl succinate (blank). The difference F (=F2-F1) of the average writing resistance values ​​is preferably 0.2g or more, more preferably 0.8g or more, and even more preferably 1.8g or more. When the difference in average writing resistance values ​​satisfies the above, it can be said that the writing experience is smooth. The average writing resistance value corresponds to the average of the writing resistance values ​​of three ballpoint pens according to the present invention, measured by the measurement method described later.

[0069] The writing resistance value of the ink composition is the average of the writing resistance values ​​measured every 0.05 seconds while writing 3m on test paper A conforming to the old JIS P3201 under the following conditions, using a ballpoint pen according to the present invention set in a record-type drawing machine [for example, manufactured by Daisy Co., Ltd., product name: PL-1000]. ·Writing speed: 4m / min ·Writing angle: 70° ·Writing load: If the diameter of the ball used in the ballpoint pen exceeds 0.3 mm: 100 gf If the diameter of the ball used in the ballpoint pen is 0.3 mm or less: 50 gf

[0070] The viscosity of the ink composition according to the present invention is not particularly limited. At a temperature of 20°C, with a rotational speed of 1 rpm (shear speed of 3.84 sec), -1 When measured under the following conditions, the range is preferably 50 to 2000 mPa·s, more preferably 100 to 1500 mPa·s, and even more preferably 150 to 1000 mPa·s. Also, in an environment of 20°C, with a rotational speed of 100 rpm (shear speed of 384 sec), -1 When measured under the conditions specified above, 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. Having the viscosity within the above range allows for a high level of stability of the ink composition and smooth flow of the ink within the ballpoint pen mechanism. The viscosity was measured using a rheometer (e.g., TA Instruments, product name: DHR-2) with the ink composition placed at 20°C and a shear rate of 3.84 sec. -1 , or 384sec -1 These are values ​​measured under the following conditions.

[0071] The surface tension of the ink composition according to the present invention is not particularly limited. At a temperature of 20°C, it is preferably in the range of 20 to 50 mN / m, more preferably 25 to 40 mN / m. Having the surface tension within this range makes it easy to suppress bleeding of writing lines and show-through to the paper surface, and also improves the wettability of the ink to the paper surface. The surface tension was measured using a surface tension meter (e.g., Kyowa Interface Science Co., Ltd., product name: DY-300) with the ink composition placed in a 20°C environment, using the vertical plate method with a platinum plate.

[0072] [Ballpoint pen] The ink composition according to the present invention is used in a ballpoint pen refill or ballpoint pen, which is equipped with a ballpoint pen tip and an ink filling mechanism.

[0073] A ballpoint pen tip consists of a tip body and a ball provided at the front end of the tip body. Examples of ballpoint pen tips include a tip in which a ball is held in a ball-holding portion formed by pressing the tip area of ​​a tip body made of a metal pipe inward from the outer surface; a tip in which a ball is held in a ball-holding portion formed by cutting a metal tip body with a drill or the like; a tip in which a resin ball seat is provided inside a metal or plastic tip body; or a tip in which the ball held in the tip is biased forward by a spring.

[0074] The material of the tip body and ball is not particularly limited, and examples include cemented carbide, stainless steel, ruby, ceramic, resin, rubber, etc. Furthermore, the ball may be subjected to surface treatment such as DLC coating.

[0075] 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, and 0.2 to 1 mm being preferred in that order. Furthermore, the ballpoint pen tip can be configured to have a resilient member inside the tip that springs the rear end of the ball forward, so that when not writing, the ball is pressed against the inner edge of the tip, creating a tight seal, and when writing, the pressure of writing causes the ball to retract, allowing ink to flow out, thereby suppressing ink leakage when not in use. The resilient member can be exemplified by a thin metal wire spring, a spring with a straight section (rod section) at one end, or a linear plastic processed body, and is configured to be able to press with a resilient force of 5 to 40 g.

[0076] Generally, in ballpoint pens with small diameter balls, the space between the tip body and the ball at the front end of the tip body is narrow, and microcapsule pigments with a larger average particle size than general-purpose pigments, or precipitated and / or aggregated colorants, tend to hinder the rotation of the ball and are difficult to dispense from the writing tip. However, in the ink composition according to the present invention, the alkenyl succinate suppresses the precipitation and / or aggregation of colorants, and in particular, by adsorbing onto the surface of the pigment (including microcapsule pigments), it has the effect of making it less likely to hinder the rotation of the ball. Furthermore, because the alkenyl succinate suppresses the precipitation and / or aggregation of colorants, the colorant is more easily dispensed from the writing tip. Therefore, it is preferable to use it in ballpoint pens or ballpoint pen refills with small diameter balls, especially ballpoint pens or ballpoint pen refills with balls with a diameter of 0.3 to 0.5 mm.

[0077] The ink filling mechanism is not particularly limited; for example, an ink container capable of being filled with ink can be used. As the ink container, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body can be used. In addition, to prevent the ink being degraded by oxygen, a molded body made of a resin with low oxygen permeability can also be used. Examples of resins with low oxygen permeability include ethylene-vinyl alcohol copolymer, polyvinylidene chloride, acrylonitrile resin, and polyester. The ink container may have a single-layer structure or a multi-layer structure.

[0078] A ballpoint pen refill (hereinafter sometimes referred to as "refill") can be formed by directly connecting a ballpoint pen tip to an ink reservoir or via a connecting member, and by directly filling the ink reservoir with ink. A ballpoint pen can be formed by housing this refill inside the barrel.

[0079] An ink backflow prevention device is placed at the trailing end of the ink that is filled into the ink container. Examples of ink backflow prevention devices include liquid stoppers and solid stoppers. The stopper consists of a non-volatile liquid and / or a low-volatility 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. These can be used individually or in combination of two or more. Examples of solid stoppers include those made of polyethylene, polypropylene, polymethylpentene, and the like. The ink backflow prevention device may consist of both a liquid stopper and a solid stopper.

[0080] For non-volatile and / or low-volatile liquids, it is preferable to add a thickening agent to increase the viscosity to a suitable level. Examples of thickening agents include clay-based thickeners such as silica with a hydrophobic surface treatment, fine silica particles with a methylated surface treatment, aluminum silicate, swellable mica, hydrophobic bentonite and montmorillonite; fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate; tripenzylidene sorbitol; fatty acid amides; amide-modified polyethylene wax; hydrogenated castor oil; dextrin compounds such as fatty acid dextrins; and cellulose compounds.

[0081] The barrel itself can be used as the ink filling mechanism, and ink can be directly filled into the barrel. By attaching a ballpoint pen tip to the front end of the barrel, a ballpoint pen equipped with both a ballpoint pen tip and an ink filling mechanism can be formed. The rear end of the ink may be filled with the above-mentioned ink backflow prevention material.

[0082] If the ink to be filled into the ink filling mechanism is of low viscosity, a ballpoint pen comprising a ballpoint pen tip and an ink filling mechanism may further include an ink supply mechanism for supplying the ink to be filled into the ink filling mechanism to the pen tip.

[0083] The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that uses an ink guide core made of a fiber bundle or the like as an ink flow rate regulator to supply ink to the pen tip; (2) a mechanism that uses a comb-shaped ink flow rate regulator to supply ink to the pen tip; and (3) a mechanism that supplies ink via a pen nib. The pen nib consists of numerous discs arranged in parallel at comb-shaped intervals, with slit-shaped ink guide grooves and ventilation grooves wider than the guide grooves that penetrate the discs axially, and an ink guide core positioned at the center of the shaft to guide ink from the ink filling mechanism to the pen tip.

[0084] The material of the pen tip is not particularly limited as long as it is a synthetic resin that can be injection molded into a structure with numerous disc-shaped grooves. Acrylonitrile-butadiene-styrene copolymer (ABS resin) is preferably used because it has high moldability and makes it easy to obtain the desired pen tip performance.

[0085] Specific examples of ballpoint pen configurations for containing the ink composition according to the present invention include: (1) a ballpoint pen having an ink reservoir filled with ink inside the barrel, to which a ballpoint pen tip is connected directly or via a connecting member, and an ink backflow prevention body is filled on the end face of the ink; (2) a ballpoint pen in which ink is directly filled inside the barrel, and a mechanism is provided to supply ink to the pen tip by interposing an ink flow control body consisting of a comb-shaped ink flow control body or an ink guide core made of a fiber bundle or the like as an ink flow control body; (3) a ballpoint pen in which ink is directly filled inside the barrel, and a mechanism is provided to supply ink to the pen tip via the above-mentioned pen core; and (4) a ballpoint pen in which ink is directly filled inside the barrel, a ballpoint pen tip is fixed to the front end of the barrel, and an ink backflow prevention body is filled on the end face of the ink.

[0086] If the ballpoint pen according to the present invention is directly filled with ink, an agitator, such as an agitator ball, may be incorporated into the barrel or ink container in which the ink is filled, in order to facilitate the redispersion of the coloring agent (particularly pigment or microcapsule pigment). Examples of the shape of the agitator include a spherical body, a rod-shaped body, etc. The material of the agitator is not particularly limited, and examples include metal, ceramic, resin, glass, etc.

[0087] The ink filling mechanism for a ballpoint pen according to the present invention may be a cartridge type that uses an ink cartridge that is pre-filled with ink and can be detachably replaced and attached to the ballpoint pen body. In this case, after the ink in the ballpoint pen's ink cartridge is used up, the ballpoint pen can be used again by replacing it with a new ink cartridge. The ink cartridge can be either one that connects to the ballpoint pen body and also serves as the barrel of the ballpoint pen, or one that covers and protects the barrel (rear barrel) after it has been connected to the ballpoint pen body. In the latter case, the ballpoint pen body and the ink cartridge may be connected, or the ink cartridge may be housed inside the barrel in a disconnected state so that the user can connect it when using the ballpoint pen to start use.

[0088] The ballpoint pen according to the present invention is equipped with a cap that covers the pen tip (writing tip), thereby preventing contamination or damage to the writing tip. Furthermore, by incorporating a retractable mechanism within the barrel that allows the writing tip to extend and retract from the barrel, it is possible to prevent the writing tip from becoming contaminated or damaged.

[0089] Any retractable ballpoint pen can be used if its writing tip is housed within the barrel and the writing tip protrudes from the barrel when the retraction mechanism is activated. Examples of retractable / retractable mechanisms include: (1) a side-slide type retractable / retractable mechanism in which an operating part (clip) that can move in the front-to-back direction is provided protruding radially outward from the rear side wall of the barrel, and the writing tip is extended and retracted from the front end opening of the barrel by sliding the operating part forward; (2) a rear-end knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part provided at the rear end of the barrel forward; (3) a side-knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part that protrudes from the outer surface of the barrel side wall radially inward; and (4) a rotary (twist) type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by rotating an operating part at the rear of the barrel.

[0090] The form of the ballpoint pen is not limited to the configuration described above, and may be a multi-function ballpoint pen (double-ended, or with a retractable tip, etc.). Examples of multi-function ballpoint pens include (1) a ballpoint pen equipped with tips of different shapes, (2) a ballpoint pen equipped with tips that dispense ink of different shades or hues, and (3) a ballpoint pen equipped with tips of different shapes, in which the ink dispensed from each tip is of different shades or hues.

[0091] When the coloring agent contains a reversible thermochromic microcapsule pigment, the writing formed on the writing surface using the ballpoint pen according to the present invention can be discolored by rubbing with a finger or by using a heating or cooling device.

[0092] Examples of heating devices include electrically heated color change devices equipped with resistance heating elements such as PTC elements, heated color change devices filled with a medium such as hot water, heated color change devices using steam or laser light, hair dryers, hot air devices, box-type heating devices, etc. Friction members and friction bodies are preferred because they can change color using a simple method.

[0093] Examples of cooling devices include chilled water, ice water, electrically charged cooling devices using Peltier elements, cooling devices filled with refrigerants such as chilled water or ice chips, air coolers, box-type cooling devices, cold storage agents, refrigerators, freezers, and the like.

[0094] The friction member and friction body are not particularly limited as long as they generate frictional heat when rubbing against the writing. For example, they may be plastic, foam, stone, wood, metal, cloth, etc. Elastic materials such as elastomers and plastic foams are preferred because they are highly elastic and can generate frictional heat by creating appropriate friction when rubbed. Although a general eraser used to erase pencil marks can be used as the friction member and friction body, eraser residue is generated when rubbing, so the above-mentioned friction member and friction body that generate almost no eraser residue are preferably used.

[0095] Examples of materials for friction members and friction bodies include silicone resin and styrene-ethylene-butadiene-styrene block copolymer (SEBS resin). Silicone resin tends to adhere to areas erased by rubbing, and the ink tends to be repelled when writing repeatedly; therefore, SEBS resin is more preferably used.

[0096] The above-described friction member or friction body can be made highly portable by being installed in a ballpoint pen. Furthermore, a ballpoint pen set can be obtained by combining a ballpoint pen with a separate friction member or friction body of any shape.

[0097] 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 without a writing tip).

[0098] In the case of a ballpoint pen provided with an actuating mechanism, the location where the friction member or friction body is provided is not particularly limited. For example, the shaft cylinder itself can be formed by a friction member, or when a clip is further provided, the clip itself can be formed by a friction member, or a friction member or friction body can be provided near the front end of the shaft cylinder, at the rear end of the shaft cylinder (the part where the writing tip is not provided), or at the knock part.

Example

[0099] Examples are shown below. Unless otherwise specified, "parts" in the examples indicate "parts by mass".

[0100] Example 101 [Preparation of Ink Composition] 25 parts of a reversible thermochromic microcapsule pigment (pre-cooled to -20°C or lower and developed to blue), and C 16 ~C 18 0.9 part of dipotassium alkenyl succinate [manufactured by Kao Corporation, product name: Latemul ASK (solid content: 28%)], 0.2 part of a shear-thinning viscosity-imparting agent (sucsinoglycan) [manufactured by Sankyo Co., Ltd., product name: Reothan], 5 parts of glycerin, 2 parts of dextrin [manufactured by Sanwa Starch Industry Co., Ltd., product name: Sandek 70], 0.5 part of a phosphate ester surfactant [manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Pliserf AL], 0.2 part of triethanolamine, 0.2 part of a preservative [manufactured by Arksey Japan Co., Ltd., product name: Proxel XL-2(S)], and 66 parts of water were mixed to prepare an ink composition. The content rate of the alkenyl succinate with respect to the total mass of the ink composition was 0.25%.

[0101] [Production of Writing Instrument] The ink composition of Example 10 was suction-filled into an ink container made of a polypropylene pipe, and then connected to a ballpoint pen tip holding a 0.5 mm diameter cemented carbide ball at the tip through a resin holder. Next, from the rear end of the ink container, an ink backflow prevention body (liquid plug) having viscoelasticity mainly composed of polybutene was filled, and a tail plug was further fitted to the rear part of the pipe, and degassing treatment was performed by centrifugation to obtain a ballpoint pen refill. Next, the above refill was incorporated into the barrel to create a writing instrument (a retractable ballpoint pen). The ballpoint pen described above has a structure in which the tip of the ballpoint pen refill is housed inside the barrel with the tip exposed to the outside air, and the tip protrudes from the opening at the front of the barrel by the operation of a clip-shaped retraction mechanism (slide mechanism) located on the rear side wall of the barrel. SEBS resin is attached to the rear end of the barrel as a friction member. In the same manner, three writing instruments were made.

[0102] The ink compositions of Examples 102 to 109 and Comparative Example 101 were prepared in the same manner as in Example 101, except that the types and amounts of materials used were changed as shown in Table 1 below. The alkenyl succinate content in each ink composition is as shown in Table 1. Three writing instruments were prepared in the same manner as in Example 101.

[0103] The ink compositions of Examples 201-205, 301-303, and Comparative Examples 201 and 301 were prepared in the same manner as in Example 101, except that the types and amounts of materials used were changed as shown in Table 2 below. The alkenyl succinate content in each ink composition is as shown in Table 2. Three writing instruments were prepared in the same manner as in Example 101, except that the diameter of the ball was changed to that shown in Table 2 below.

[0104] Example 401 [Preparation of ink composition] 34 parts of a black pigment dispersion [carbon black, acrylic copolymer, and water mixed in a bead mill (solids content: 27%)] and C 16 ~C 18An ink composition was prepared by mixing 1.8 parts of dipotassium alkenylsuccinate [manufactured by Kao Corporation, product name: Latemul ASK (solids content: 28%)], 0.2 parts of shear viscosity reducer (succinoglycan) [manufactured by Sansho Co., Ltd., product name: Leozan], 5 parts of glycerin, 2 parts of dextrin [manufactured by Sanwa Starch Industry Co., Ltd., product name: Sandec 70], 0.5 parts of phosphate ester surfactant [manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Prisurf AL], 0.2 parts of triethanolamine, 0.2 parts of preservative [manufactured by Arcsarda Japan Co., Ltd., product name: Proxel XL-2(S)], and 56.1 parts of water. The content of alkenylsuccinate relative to the total mass of the ink composition was 0.5%.

[0105] [Manufacturing of writing instruments] The ink composition of Example 401 was suction-filled into an ink container made of polypropylene pipe, and then connected to a ballpoint pen tip holding a 0.4 mm diameter carbide ball at its tip via a resin holder. Next, a viscoelastic ink backflow prevention body (liquid stopper) mainly composed of polybutene was filled into the rear end of the ink container, and a tail plug was fitted to the rear of the pipe. Degassing was performed by centrifugation to obtain a ballpoint pen refill. Next, the above refill was incorporated into the barrel to create a writing instrument (a retractable ballpoint pen). The ballpoint pen described above has a structure in which the tip of the ballpoint pen refill is housed inside the barrel while exposed to the outside air, and the tip protrudes from the opening at the front of the barrel by pressing the operating part located at the rear end of the barrel forward. In the same manner, three writing instruments were made.

[0106] The ink compositions of Examples 402 and 403, and Comparative Examples 401 and 402, were prepared in the same manner as Example 401, except that the types and amounts of materials used were changed as shown in Table 3 below. The alkenyl succinate content in each ink composition is as shown in Table 3. Three writing instruments were prepared in the same manner as in Example 401.

[0107] The ink compositions of Examples 501-504 and Comparative Examples 501-503 were prepared in the same manner as in Example 401, except that the types and amounts of materials used were changed as shown in Table 3 below. The alkenyl succinate content in each ink composition is as shown in Table 3. Three writing instruments were prepared in the same manner as in Example 401, except that the diameter of the ball was changed to that shown in Table 3 below.

[0108] [Table 1]

[0109] [Table 2]

[0110] [Table 3]

[0111] The materials listed in Tables 1, 2, and 3 are the materials shown below. (1) Those that have been pre-cooled to below -20°C to produce a blue color. (2) A mixture of carbon black, acrylic copolymer, and water, prepared using a bead mill (solids content: 27%) (3) Manufactured by Orient Chemical Industries, Ltd., Product name: Water Blue 105 (4)C 16 ~C 18 Dipotassium alkenyl succinate salt [Manufactured by Kao Corporation, Product name: Latemul ASK (Solid content: 28%)] (5) Succinoglycan [Manufactured by Sansho Co., Ltd., Product name: Leozan] (6) A polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid (solids content: 30%) (7) Manufactured by Sanwa Starch Industry Co., Ltd., Product name: Sandec 70 (8) Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Product name: Prysurf AL (9) Manufactured by Arcsarda Japan Co., Ltd., Product name: Proxel XL-2(S)

[0112] The above-mentioned reversible thermochromic microcapsule pigment was prepared as follows. [Preparation of reversible thermochromic microcapsule pigments] A reversible thermochromic composition consisting of (a) 2 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindole-3-yl) as component (a), 8 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as component (b), and 50 parts of 4-benzyloxyphenylethyl capric acid as component (c) was added to a mixed solution consisting of 35 parts of aromatic isocyanate prepolymer as a wall material and 40 parts of a co-solvent. The mixture was then emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution, and after stirring continued while heating, 2.5 parts of a water-soluble aliphatic modified amine were added, and stirring was continued to prepare a microcapsule dispersion. A reversible thermochromic microcapsule pigment with an average particle size of 1.9 μm was obtained from the above microcapsule dispersion by centrifugation. The reversible thermochromic microcapsule pigment 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 changes.

[0113] [Writing resistance measurement] The writing instruments prepared in each example and comparative example were set in a record-type drawing machine [manufactured by Daisy Co., Ltd., product name: PL-1000] at room temperature (20°C), and 3m circles were drawn on test paper A conforming to the old JIS P3201 under the following conditions. The average value was calculated from the writing resistance values ​​measured every 0.05 seconds. The same measurement was performed on the three writing instruments in each example and comparative example, and the average value was calculated from the writing resistance values ​​of each of the three writing instruments, and this was taken as the average writing resistance value. ·Writing speed: 4m / min ·Writing angle: 70° ·Writing load: If the diameter of the ball used in the ballpoint pen exceeds 0.3 mm: 100 gf If the diameter of the ball used in the ballpoint pen is 0.3 mm or less: 50 gf

[0114] [Writability Evaluation] A written test, described below, was administered to 20 randomly selected participants. (Written exam) Using the ballpoint pen prepared in Comparative Example 101 as a blank, at room temperature (20°C), 12 oval-shaped circles (approximately 15 mm in major axis and 8 mm in minor axis) were handwritten in a spiral pattern per line on an A4-sized test sheet (portrait orientation), perpendicular to the long side (horizontal direction), with the circles touching each other. Then, using the ballpoint pens prepared in Examples 101-109, writing was performed using the same test method as above. The writing feel of Examples 101-109 compared to Comparative Example 101 (blank) was evaluated on a four-point scale according to the following criteria. The writing feel of Examples 201-205 compared to Comparative Example 201 (blank), and the writing feel of Examples 301-303 compared to Comparative Example 301 (blank) were evaluated in the same manner as above. Furthermore, the writing feel of Examples 401 and 402 compared to Comparative Example 401, the writing feel of Example 403 compared to Comparative Example 402 (blank), the writing feel of Examples 501 and 502 compared to Comparative Example 501 (blank), the writing feel of Example 503 compared to Comparative Example 502 (blank), and the writing feel of Example 504 compared to Comparative Example 503 (blank) were evaluated in the same manner as described above. For the test paper, writing paper A conforming to the old JIS P3201 was used. 3: The writing instrument in the example provided a very smooth writing experience on the blank. 2: The writing instrument in the example provided a smooth writing experience on the blank. 1: The writing instrument in the example had a slightly smoother writing feel compared to the blank. 0: The writing instrument in the example had a writing quality that was no different from or inferior to that of the blank.

[0115] The scores based on each monitor's evaluation were totaled, and writing ability was assessed according to the following criteria. The evaluation results are shown in Tables 4, 5, and 6. A rating of "A" to "C" was considered a passing grade. A: The total score is between 46 and 60. B: The total score is between 31 and 45. C: The total score is between 16 and 30. D: The total score is between 0 and 15.

[0116] [Table 4]

[0117] [Table 5]

[0118] [Table 6] [Explanation of symbols]

[0119] T1 Full Color Temperature T2 color development start temperature t3 decolorization start temperature t4 complete color erasure temperature T1 complete decolorization temperature T2 decolorization start temperature T3 color development start temperature T4 Full Color Temperature ΔH Hysteresis width

Claims

1. A water-based ink composition for ballpoint pens comprising a coloring agent, an alkenyl succinate, and water.

2. The ink composition according to claim 1, wherein the alkenyl succinate is dipotassium alkenylsuccinate.

3. The ink composition according to claim 1, wherein the content of the alkenyl succinate with respect to the total mass of the ink composition is in the range of 0.2 to 5% by mass.

4. The ink composition according to claim 1, wherein the coloring agent is a pigment.

5. The ink composition according to claim 4, wherein the pigment comprises 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 that determines the temperature at which the color reaction of components (a) and (b) occurs.

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

7. A refill containing the ink composition according to any one of claims 1 to 5.

8. The ballpoint pen according to claim 6, wherein the diameter of the ball provided at the writing tip of the ballpoint pen is 0.3 to 0.5 mm.

9. The refill according to claim 7, wherein the diameter of the ball provided at the writing tip of the refill is 0.3 to 0.5 mm.

Images