JP2020002290A - Aqueous ink composition for reversible thermochromic writing instrument and writing instrument using the same - Google Patents

Abstract

To provide an aqueous ink composition for a reversible thermochromic writing instrument that has good dispersion stability, is excellent in storage stability of the ink composition and when used in writing instrument, is excellent in writing performance, dryness of handwriting and dry-up resistant performance and to provide a writing instrument using the aqueous ink composition.SOLUTION: The aqueous ink composition for a reversible thermochromic writing instrument includes two or more kinds of reversible thermochromic microcapsule pigments different in specific gravity, a polymer including a specific structure in the constitutional unit, glycerin, an inorganic salt of a monovalent cation and water. The writing instrument uses the aqueous ink composition.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water-based ink composition for a reversible thermochromic writing instrument. More specifically, the present invention relates to a reversible thermochromic aqueous ink composition having excellent pigment dispersion stability. The present invention also relates to a writing instrument using the composition.

  Conventionally, a water-based ink composition for a reversible thermochromic writing instrument using a microcapsule pigment has been proposed. The ink using the microcapsule pigment has a problem in the storage stability of the ink during long-term storage. Therefore, it is proposed to use a so-called gel ink containing a shear thinning agent, or to use a water-soluble polymer coagulant to form a loose agglomerate that can be redispersed even when the pigment settles out. Have been. Further, there is known an ink composition comprising a microcapsule pigment, microcapsule particles having a specific gravity different from that of the microcapsule pigment, and a vehicle containing water and a polymer coagulant, wherein the specific gravity of the vehicle is adjusted (Patent Document 1). . However, the above-mentioned ink composition is not sufficient to suppress sedimentation by making the microcapsule pigment and the microcapsule particles into a loose aggregate using a polymer flocculant, but this is not sufficient, and there is room for improvement in the conventional techniques.

  As described above, the conventionally proposed inks have a limitation in writing implements used in the case of gel inks due to the high ink viscosity, and in low-viscosity inks, microcapsule pigments and microcapsule particles are loosely aggregated by a polymer flocculant. Although it is not enough to suppress sedimentation as a body, it was not satisfactory enough when used for a writing instrument, for example, it was necessary to provide a re-stirring mechanism in the ink container.

JP 2007-224295 A

  The water-based ink composition for reversible thermochromic writing implements of the present invention has excellent dispersion stability, excellent storage stability of the ink composition, and excellent writing performance, handwriting dryness, and dry-up resistance even when used in a writing implement. It is an object of the present invention to provide an object and a writing instrument using the same.

The present invention relates to a water-based ink composition for a reversible thermochromic writing implement (hereinafter, sometimes referred to as a "water-based ink composition for a writing implement" or an "aqueous ink composition", an "ink composition", or a "composition". ), A polymer containing 2-methacryloyloxyethylphosphorylcholine in a structural unit (hereinafter, sometimes referred to as “MPC polymer”), glycerin, and an inorganic salt of a monovalent cation (hereinafter, sometimes referred to as “MPC polymer”). , "Inorganic salt" may be used in combination.
That is, the present invention
"1. (a) a component comprising an electron-donating color-forming organic compound;
(B) a component comprising an electron-accepting compound;
(C) a reaction medium that reversibly causes an electron transfer reaction by the components (a) and (b) in a specific temperature range;
A reversible thermochromic microcapsule pigment containing a reversible thermochromic composition comprising:
A polymer containing 2-methacryloyloxyethyl phosphorylcholine in a structural unit,
A reversible thermochromic pigment comprising glycerin, a monovalent inorganic salt of a cation, and water, wherein the reversible thermochromic microcapsule pigment comprises two or more microcapsule pigments having different specific gravities. A water-based ink composition for writing implements.
2. The composition according to claim 1, wherein the content of the inorganic salt of the monovalent cation is 1 to 10% by mass based on the total mass of the aqueous ink composition.
3. 3. The composition according to claim 1 or 2, wherein the content of glycerin is larger on a mass basis than the content of the inorganic salt of a monovalent cation.
4. The composition according to any one of claims 1 to 3, wherein the inorganic salt of a monovalent cation is a halide of an alkali metal.
5. Item 5. The composition according to any one of Items 1 to 4, wherein the viscosity measured at 20 rpm at 20 rpm and an EL viscometer is 1 to 20 mPa · s.
6. A writing instrument comprising the composition according to any one of Items 1 to 5. About.

  According to the present invention, even when the reversible thermochromic ink composition contains two or more types of microcapsule pigments having different specific gravities, the polymer containing 2-methacryloyloxyethylphosphorylcholine as a constituent unit, glycerin, and monovalent By containing the inorganic salt of a cation in the vehicle, the dispersion of the microcapsule pigment can be stably maintained without floating or sedimentation even in a low-viscosity ink. Furthermore, the microcapsule pigment can be stably dispersed without using a re-stirring mechanism such as a stirrer when used in a writing instrument, and thus can be used in various writing instruments. In addition, when used in a writing instrument, because the pigment does not float or settle, there is no spot on the handwriting, because it has a uniform dispersion and moisturizing effect, Excellent effects such as stable writing performance are obtained without blurring of handwriting.

4 is a graph illustrating a hysteresis characteristic in a color density-temperature curve of a heat-decolorable reversible thermochromic composition used in the present invention.

  Hereinafter, embodiments of the present invention will be described in detail. In the present specification, “parts”, “%”, “ratio”, and the like indicating the blending are based on mass unless otherwise specified.

The reversible thermochromic aqueous ink composition according to the present invention comprises two or more kinds of microcapsule pigments having different specific gravities, a polymer containing 2-methacryloyloxyethyl phosphorylcholine in a constitutional unit, glycerin, a monovalent cation inorganic salt, and water. And
In the present invention, the ink composition contains a polymer containing 2-methacryloyloxyethyl phosphorylcholine as a constituent unit, glycerin, and a monovalent cation inorganic salt to stably produce two or more types of microcapsule pigments having different specific gravities. Can be dispersed.
Hereinafter, each component constituting the aqueous ink composition according to the present invention will be described.

(Polymer containing 2-methacryloyloxyethyl phosphorylcholine in the structural unit)
The reversible thermochromic aqueous ink composition according to the present invention comprises a polymer containing 2-methacryloyloxyethyl phosphorylcholine in a constitutional unit. The polymer containing 2-methacryloyloxyethyl phosphorylcholine as a constituent unit used in the present invention acts on the surface of the microcapsule, and stably and uniformly disperses two or more kinds of microcapsule pigments having different specific gravities. Is made possible. Specific examples of the MPC polymer include a single polymer having 2-methacryloyloxyethyl phosphorylcholine as a constitutional unit, a polymer having 2-methacryloyloxyethyl phosphorylcholine as a constitutional unit, and a polymer having another 2-methacryloyloxy as a constitutional unit. And the like. More specifically, as other polymers containing 2-methacryloyloxy in the structural unit, 2-methacryloyloxybutyl, 2-methacryloyloxystearyl, sodium methacrylate, 2-methacryloyloxy-β-hydroxypropyltrimethylammonium chloride and the like And two or more of these may be used. More specifically, examples include LIPIDURE-HM, LIPIDURE-PMB, LIPIDURE-A, LIPIDURE-B, LIPIDURE-C, LIPIDURE-S, and LIPIDURE-NR (all of which are trade names manufactured by NOF CORPORATION).

  The mixing ratio of the MPC polymer is preferably 0.1% by mass to 10% by mass, more preferably 0.3% by mass to 3.0% by mass, based on the total mass of the ink composition. If the amount is less than this range, it is difficult to obtain the desired stability of the microcapsule pigment, and if the amount is more than this range, further improvement in the stability of the microcapsule pigment cannot be obtained. Within the above range, the microcapsule pigment can stably exist in the ink without settling or floating, and is therefore preferable.

  The aqueous ink composition for a reversible thermochromic writing instrument according to the present invention comprises glycerin. Glycerin used in the present invention functions as a humectant in addition to the specific gravity adjuster of the ink composition. The use of glycerin has a function of suppressing precipitation of a monovalent cation inorganic salt described later. Furthermore, when the ink composition is used as a humectant in a writing instrument, it also has an effect on dry-up in which the writing tip dries.

  The mixing ratio of glycerin is preferably 1% by mass to 30% by mass, more preferably 5% by mass to 25% by mass, based on the total mass of the ink composition. When the amount is less than this range, it becomes difficult to suppress the precipitation of an inorganic salt described later, and when the amount is more than this range, not only does the ink viscosity become high, disturbing the ejection but also the handwriting tends to be hard to dry. It is preferable that the content is in the above-mentioned range, since it is possible to suppress the precipitation of the inorganic salt while maintaining an appropriate ink viscosity and contribute to the adjustment of the specific gravity of the ink vehicle.

  The aqueous ink composition for a reversible thermochromic writing implement according to the present invention further comprises a monovalent cation inorganic salt. The inorganic salt functions as a specific gravity adjuster of the ink composition. By adding a monovalent cation inorganic salt, sedimentation can be suppressed even for a microcapsule pigment having a relatively large specific gravity. As the monovalent cation inorganic salt used in the present invention, the cation is preferably an alkali metal. Specifically, lithium, sodium, potassium, rubidium, cesium and the like can be mentioned. More specific inorganic salts of monovalent cations include the above-mentioned alkali metal halides and sulfates. Lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, lithium bromide, lithium bromide, Sodium iodide, potassium bromide, rubidium bromide, cesium bromide, lithium iodide, sodium iodide, potassium iodide, rubidium iodide, cesium iodide, lithium sulfate, sodium sulfate, potassium sulfate, rubidium sulfate, cesium sulfate, etc. Is mentioned. The purpose of adjusting the specific gravity is to adjust the specific gravity because inorganic salts of divalent or higher cations do not themselves have high water solubility, and even in a hydrated state, they easily form a poorly water-soluble salt with a specific anion to form precipitation. It is not suitable for large additions.

  The compounding ratio of the monovalent inorganic salt is preferably from 1% by mass to 10% by mass, more preferably from 3% by mass to 8% by mass, based on the total mass of the ink composition. If the amount is less than this range, it is difficult to adjust the specific gravity of the vehicle to a desired value. If the amount is more than this range, precipitation tends to occur even when the writing tip is slightly dried. The above range is preferable because the desired specific gravity of the vehicle can be adjusted without being precipitated by the combination with the glycerin.

The reversible thermochromic aqueous ink composition for a writing instrument according to the present invention comprises an MPC polymer, glycerin and an inorganic salt of a monovalent cation. Microcapsule pigment cannot be kept in a stable dispersed state. That is, in order to obtain a specific gravity enough to stably disperse the microcapsule pigment with glycerin, it is necessary to mix a large amount thereof, which results in an increase in ink viscosity and poor handwriting dryness. Further, the inorganic salt of a monovalent cation can increase the specific gravity to some extent without increasing the viscosity of the ink, but since the evaporation of water cannot be suppressed, the inorganic salt may be precipitated. By using a combination of glycerin and an inorganic salt, the specific gravity can be adjusted to some extent without increasing the viscosity of the ink and maintaining the moisturizing effect. However, in the case of glycerin alone, inorganic salt alone, or a combination system of glycerin and inorganic salt, when two or more types of microcapsule pigments having different specific gravities exist, some are dispersed, some are settled, some are floating, Cannot be uniformly dispersed. Therefore, the MPC polymer alone cannot be uniformly dispersed, but when the MPC polymer is blended in a combined system of glycerin and an inorganic salt, the MPC polymer acts on the microcapsule pigment, and two or more types of microcapsules having different specific gravities are used. The pigment can be prevented from floating or settling, and can be uniformly dispersed.
As described above, a stable dispersion state can be maintained even in a low-viscosity ink by using the three components together.

  The aqueous ink composition for a reversible thermochromic writing instrument according to the present invention uses two or more types of reversible thermochromic microcapsule pigments having different specific gravities. The so-called gel ink has a uniform dispersion state without floating and sedimentation. However, in an aqueous solution whose specific gravity is adjusted, it shows different behavior such as floating and sedimentation.

Specifically, the materials and compositions included in the microcapsule pigment, the shape of the microcapsules, the particle size, the film material of the microcapsule wall film, the film thickness, the ratio between the inclusions and the wall film, and the like, differ in specific gravity. It is given as a thing.

  The reversible thermochromic microcapsule pigment that can be used in the present invention will be described below. Examples of the reversible thermochromic microcapsule pigment include a specific temperature (discoloration point) described in JP-B-51-44706, JP-B-51-44707, and JP-B-1-29398. Discolored before and after that, a decolored state in the temperature range above the high-temperature side discoloration point, a color-developed state in the temperature range below the low-temperature side discoloration point, and only one specific state exists in the normal temperature range of the two states. The other state is maintained while the heat or cold required to develop the state is applied, but returns to the state exhibited in the normal temperature range when the heat or cold is not applied, the hysteresis width. Applying a reversible thermochromic microcapsule pigment enclosing a reversible thermochromic composition (decolored by heating and colored by cooling) having a relatively small characteristic (ΔH = 1 to 7 ° C.) Yes (Figure 1 Irradiation).

Further, large hysteresis characteristics (ΔH _B = 8 to 50 ° C.) described in Japanese Patent Publication No. 4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936 and the like. ), That is, when the shape of the curve plotting the change in the coloring density due to the temperature change is such that the temperature rises from a temperature lower than the color change temperature range, and conversely, it decreases from a temperature higher than the color change temperature range. The color changes in a low temperature range below the full color development temperature (t ₁ ), or the decoloration state in a high temperature range above the complete decolorization temperature (t ₄ ). Heat-decoloring type (decolorizes by heating and develops color by cooling) reversible thermochromic composition having a color memory in the [temperature range between t _{2 and} t ₃ (substantially two-phase holding temperature range)] Reversible thermochromic micros Capsule pigments can also be applied (see FIG. 2).

  Hereinafter, the hysteresis characteristics in the color density-temperature curve of the microcapsule pigment containing the reversible thermochromic composition will be described with reference to the graph of FIG.

In FIG. 2, the vertical axis represents color density, and the horizontal axis represents temperature. The change in color density due to the temperature change proceeds along the arrow. Here, A is a point indicating a density at a temperature t ₄ (hereinafter, referred to as a complete decoloring temperature) at which a completely decolored state is reached, and B is a temperature t ₃ at which decoloring starts (hereinafter, a decoloring start temperature). C) is a point indicating the density at a temperature t ₂ at which color development starts (hereinafter, referred to as a color development start temperature), and D is a temperature t ₁ (hereinafter, referred to as a color development start temperature). , The full color development temperature).

  The length of the line segment EF is a measure of the contrast of discoloration, and the length of the line segment HG is a temperature width (hereinafter referred to as a hysteresis width ΔH) indicating the degree of hysteresis. It is easy to maintain each state before and after discoloration.

Here, the difference between t ₄ and t ₃ or the difference (Δt) between t ₂ and t ₁ is a measure of the sharpness of discoloration.

Furthermore, in the normal temperature range, only one specific state (color-developed state) of the reversible thermochromic composition is present in a normal temperature range, and handwriting by the reversible thermochromic composition is easily performed by frictional heat generated by friction. For discoloring (decoloring), it is preferable that the complete decoloring temperature (t ₄ ) is 50 to 95 ° C. and the color development start temperature (t ₂ ) is −50 to 10 ° C.

Here, the color development state can be maintained in the normal temperature range, and the complete decoloring temperature (t ₄ ) is 50 to 95 ° C. and the color development start temperature (t ₂ ) in order to facilitate discoloration due to friction of handwriting. When the heating is stopped in a state where the temperature does not reach the complete decoloring temperature (t ₄ ) from the color developing state through the decoloring start temperature (t ₃ ), the first state is returned again. When the cooling is stopped in a state where the temperature does not reach the full color development temperature (t ₁ ) from the decolored state through the color development start temperature (t ₂ ), the color development state is maintained. Therefore, if the complete decoloring temperature (t ₄ ) is 50 ° C. or higher, which is higher than the normal temperature range, the color development state is maintained in a normal use state, and the color development start temperature (t ₂ ) is lower than the normal temperature range. Decolored state is maintained in normal use if the temperature is -50 to 10 ° C Is done.

In the above-described temperature setting of the complete decoloring temperature (t ₄ ), it is preferable that the temperature be higher in order to maintain the coloring state in a normal use state, and that the frictional heat due to friction reduces the complete decoloring temperature ( In order to exceed t ₄ ), the temperature is preferably low. Thus, the complete decoloring temperature _{(t 4)} is preferably 50 to 90 ° C., more preferably 60-80 ° C.. Further, in the above-mentioned temperature setting of the color development start temperature (t ₂ ), in order to maintain the decolored state in a normal use state, the temperature is preferably lower, and it is preferably −50 to 5 ° C. -50 to 0 ° C is more preferable. In the present invention, the hysteresis width (ΔH) is in the range of 50 ° C to 100 ° C, preferably 55 to 90 ° C, more preferably 60 to 80 ° C.

As the microcapsule pigment that can be used in the aqueous ink composition for writing according to the present invention, a reversible thermochromic composition having a complete decoloring temperature (t ₄ ) on a higher temperature side than the above-described color changing temperature range can also be used.

In the normal temperature range of the reversible thermochromic composition, only one specific state (color developing state) is present, and the handwriting by the reversible thermochromic composition is generated by heat obtained from a heat erasing tool or the like. For erasing, the complete erasing temperature (t ₄ ) is set to 80 ° C. or higher, and the color development starting temperature (t ₂ ) is set to 15 ° C. or lower. Here, the color development state can be maintained in a normal temperature range, and the color erasure state is maintained in normal use. Therefore, the complete color erasure temperature (t ₄ ) is 80 ° C. or more, and the color development start temperature (t ₂ ). If the heating is stopped in a state where the temperature does not reach the complete decoloring temperature (t ₄ ) from the colored state through the decoloring start temperature (t ₃ ), the state returns to the first state again. And the state where the color is generated is maintained even if the cooling is stopped in a state where the temperature does not reach the full color development temperature (t ₁ ) from the decolored state through the color development start temperature (t ₂ ). If the complete decoloring temperature (t ₄ ) is equal to or higher than 80 ° C. exceeding the normal temperature range, the color development state is maintained in a high temperature environment such as in a car in summer, and the color development start temperature (t ₂ ) is 15 ° C. lower than the normal temperature range. At the following temperatures, the decolored state is maintained in normal use. Furthermore, if the complete decoloring temperature (t ₄ ) is 90 ° C. or higher, the color development state is more maintained in a high temperature environment, and if the color development start temperature (t ₂ ) is 10 ° C. or lower, the decoloration state is normal. More maintained in use. Therefore, the temperature setting is an important requirement for selecting and selectively viewing discolored handwriting on the writing surface, and the handwriting can achieve the intended purpose. In the above-mentioned temperature setting of the complete erasing temperature (t ₄ ), it is preferable that the temperature be higher in order to maintain the color development state in a high-temperature environment, and the complete erasing temperature (t ₄ ) is preferably 90. C. or higher, more preferably 100 ° C. or higher. Further, in the above-mentioned temperature setting of the color development start temperature (t ₂ ), in order to maintain the decolored state in a normal use state, the temperature is preferably lower, and it is preferably −50 to 10 ° C. -50 to 5 ° C is more preferable. In order to bring the reversible thermochromic composition into a colored state in advance, it is preferable to cool it with a general-purpose freezer as a cooling means.However, in consideration of the cooling capacity of the freezer, it is limited to −50 ° C. Therefore, the complete color development temperature (t ₁ ) is -50 ° C. or higher. In the present invention, the hysteresis width (ΔH) is in the range of 70 ° C to 150 ° C.

  By using the reversible thermochromic composition, handwriting formed on important documents and the like does not fade even when left in a high-temperature environment such as in a car in summer, and is applicable as a water-based ink composition for writing implements. Can be expanded. Further, since it is difficult to erase the image due to the rubbing by the friction member, it can be used to determine the authenticity of the document.

  Hereinafter, the components (A), (B), and (C) constituting the reversible thermochromic composition will be described.

  In the present invention, the component (a) is an electron-donating colorant that provides an electron to the component (b), which is a color developer, and forms a color by opening a ring structure such as a lactone ring of the component (a). It consists of an organic compound. Examples of such electron-donating color-forming organic compounds include diphenylmethanephthalide, phenylindolylphthalide, indolylphthalide, diphenylmethaneazaphthalide, phenylindolylazaphthalide, fluoran, and styrinoquinoline. , Diazarhodamine lactones, pyridines, quinazolines, bisquinazolines and the like.

  As the electron-accepting compound of the component (b), a compound group having an active proton, a pseudo-acid compound group (a compound group which is not an acid but acts as an acid in the composition to form the component (a) to develop a color), an electron There is a group of compounds having vacancies.

  As an example of a compound having an active proton, compounds having a phenolic hydroxyl group include monophenols to polyphenols, and further, as a substituent thereof, an alkyl group, an aryl group, an acyl group, an alkoxycarbonyl group, a carboxy group and an ester thereof. Or phenol-aldehyde condensed resins such as bis- and tris-type phenols having an amide group, a halogen group and the like. Further, a metal salt of the compound having a phenolic hydroxyl group may be used.

  The component (c) of the reaction medium which reversibly causes the electron transfer reaction by the component (a) and the component (b) in a specific temperature range includes alcohols, esters, ketones, and ethers. .

  The component (c) is preferably a color density-temperature curve, wherein a large hysteresis characteristic (a curve plotting a change in coloring density due to a temperature change) indicates a case where the temperature is changed from a low temperature to a high temperature, and a case where the temperature is changed from a high temperature to a low temperature. A carboxylic acid ester compound having a ΔT value (melting point−cloud point) of 5 ° C. or more and less than 50 ° C., which can form a reversible thermochromic composition exhibiting color memory, which changes color when it changes to the side. Used. As such a compound, various compounds have been proposed, and any compound can be arbitrarily selected and used, and specific examples thereof include the following.

（式中、Ｒ_１は水素原子又はメチル基を示し、ｍは０〜２の整数を示し、Ｘ_１、Ｘ_２のいずれか一方は−（ＣＨ_２）ｎＯＣＯＲ_２又は−（ＣＨ_２）ｎＣＯＯＲ_２、他方は水素原子を示し、ｎは０〜２の整数を示し、Ｒ_２は炭素数４以上のアルキル基又はアルケニル基を示し、Ｙ_１及びＹ_２は水素原子、炭素数１〜４のアルキル基、メトキシ基、又は、ハロゲンを示し、ｒ及びｐは１〜３の整数を示す。） First, as the component (c), a compound represented by the following general formula (1) described in JP-A-2006-137886 is preferably used.

(Wherein, R ₁ represents a hydrogen atom or a methyl group, m represents an integer of 0 to 2, and _one of X ₁ and X ₂ represents — (CH ₂ ) nOCOR ₂ or — (CH ₂ ) nCOOR ₂ The other represents a hydrogen atom, n represents an integer of 0 to 2, R ₂ represents an alkyl group or an alkenyl group having 4 or more carbon atoms, Y ₁ and Y ₂ represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms. Represents a group, a methoxy group or a halogen, and r and p represent an integer of 1 to 3.)

Among the compounds represented by the formula (1), when R ₁ is a hydrogen atom, a reversible thermochromic composition having a wider hysteresis width is preferably obtained, and further, R ₁ is a hydrogen atom; , M is more preferably 0.

（式中のＲは炭素数８以上のアルキル基又はアルケニル基を示すが、好ましくは炭素数１０〜２４のアルキル基、更に好ましくは炭素数１２〜２２のアルキル基である。） In addition, among the compounds represented by the formula (1), a compound represented by the following general formula (2) is more preferably used.

(R in the formula represents an alkyl group or alkenyl group having 8 or more carbon atoms, preferably an alkyl group having 10 to 24 carbon atoms, and more preferably an alkyl group having 12 to 22 carbon atoms.)

（式中、Ｒは炭素数８以上のアルキル基又はアルケニル基を示し、ｍ及びｎはそれぞれ１〜３の整数を示し、Ｘ及びＹはそれぞれ水素原子、炭素数１〜４のアルキル基、炭素数１〜４のアルコキシ基、ハロゲンを示す。） Further, as the component (c), a compound represented by the following general formula (3) can also be used.

(Wherein, R represents an alkyl group or alkenyl group having 8 or more carbon atoms, m and n each represent an integer of 1 to 3, X and Y each represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, It represents an alkoxy group of formulas 1 to 4 and halogen.)

  Further, a compound represented by the following general formula (4) can also be used as the component (c).

（式中、Ｘは水素原子、炭素数１〜４のアルキル基、メトキシ基、ハロゲン原子のいずれかを示し、ｍは１乃至３の整数を示し、ｎは１〜２０の整数を示す。） (A) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that reversibly causes an electron transfer reaction by the components (a) and (b) in a specific temperature range. The reversible thermochromic microcapsule pigment in which the reversible thermochromic composition comprising at least is embedded in a microcapsule will be described below.

(In the formula, X represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, and a halogen atom, m represents an integer of 1 to 3, and n represents an integer of 1 to 20.)

（式中、Ｒは炭素数１乃至２１のアルキル基又はアルケニル基を示し、ｎは１〜３の整数を示す。） Further, a compound represented by the following general formula (5) can be used as the component (c).

(In the formula, R represents an alkyl group or alkenyl group having 1 to 21 carbon atoms, and n represents an integer of 1 to 3.)

（式中、Ｘは水素原子、炭素数１〜４のアルキル基、炭素数１〜４のアルコキシ基、ハロゲン原子のいずれかを示し、ｍは１〜３の整数を示し、ｎは１〜２０の整数を示す。） Further, a compound represented by the following general formula (6) can be used as the component (c).

(In the formula, X represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a halogen atom, m represents an integer of 1 to 3, and n represents 1 to 20. Represents an integer.)

（式中、Ｒは炭素数４〜２２のアルキル基、シクロアルキルアルキル基、シクロアルキル基、炭素数４〜２２のアルケニル基のいずれかを示し、Ｘは水素原子、炭素数１〜４のアルキル基、炭素数１〜４のアルコキシ基、ハロゲン原子のいずれかを示し、ｎは０又は１を示す。） Further, a compound represented by the following general formula (7) can be used as the component (c).

(Wherein, R represents any of an alkyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, a cycloalkyl group, and an alkenyl group having 4 to 22 carbon atoms, X represents a hydrogen atom, and an alkyl having 1 to 4 carbon atoms. Group, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom, and n represents 0 or 1.)

（式中、Ｒは炭素数３〜７のアルキル基を示し、Ｘは水素原子、メチル基、ハロゲン原子のいずれかを示し、Ｙは水素原子、メチル基のいずれかを示し、Ｚは水素原子、炭素数１〜４のアルキル基、炭素数１又は２のアルコキシ基、ハロゲン原子のいずれかを示す。） Further, a compound represented by the following general formula (8) can be used as the component (c).

(Wherein, R represents an alkyl group having 3 to 7 carbon atoms, X represents any one of a hydrogen atom, a methyl group, and a halogen atom, Y represents any one of a hydrogen atom and a methyl group, and Z represents a hydrogen atom. , An alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or a halogen atom.)

Further, a compound represented by the following general formula (9) can be used as the component (c).

  In the formula (9), R represents an alkyl group having 4 to 22 carbon atoms, an alkenyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, or a cycloalkyl group, and X represents a hydrogen atom, an alkyl group, an alkoxy group. Y represents a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom, and n represents 0 or 1.

Further, a compound represented by the following general formula (10) can be used as the component (c).

  In the formula (10), R is any one of an alkyl group having 3 to 18 carbon atoms, a cycloalkylalkyl group having 6 to 11 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, and an alkenyl group having 3 to 18 carbon atoms. X represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, or a halogen atom; Y represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, methoxy Group, an ethoxy group, or a halogen atom.

Further, a compound represented by the following general formula (11) can be used as the component (c).

  In the formula (11), R represents a cycloalkyl group having 3 to 8 carbon atoms or a cycloalkylalkyl group having 4 to 9 carbon atoms, and n represents an integer of 1 to 3.

Further, a compound represented by the following general formula (12) can be used as the component (c).

  (In the formula (12), R represents an alkyl group having 3 to 17 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, or a cycloalkylalkyl group having 5 to 8 carbon atoms; X represents a hydrogen atom; To 5, an alkyl group, a methoxy group, an ethoxy group, or a halogen atom, and n represents an integer of 1 to 3.)

  Furthermore, a specific alkoxyphenol compound having a linear or side chain alkyl group having 3 to 18 carbon atoms is used as the electron accepting compound (JP-A-11-129623 and JP-A-11-5973), or Using a hydroxybenzoic acid ester (Japanese Patent Application Laid-Open No. 2001-105732) or using gallic acid ester or the like (Japanese Patent Publication No. 51-44706, Japanese Patent Application Laid-Open No. 2003-253149); A microcapsule pigment containing a reversible thermochromic composition (decolored by cooling) can also be applied (see FIG. 3).

  The proportions of the components (a), (b) and (c) depend on the density, the discoloration temperature, the discoloration form and the type of each component, but generally the desired discoloration characteristics are obtained. The component ratio is in the range of 0.1 to 50, preferably 0.5 to 20, component (b) and 1 to 800, preferably 5 to 200, component (b) with respect to component (a). All ratios are based on mass). Further, each component may be used as a mixture of two or more kinds.

  The reversible thermochromic composition is encapsulated in microcapsules and used as a reversible thermochromic microcapsule pigment. This is because the reversible thermochromic composition can be maintained under the same composition under the various use conditions and can exert the same effect.

  Examples of the method for microencapsulating the reversible thermochromic composition include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, an in-liquid curing coating method, a phase separation method from an aqueous solution, and a phase separation method from an organic solvent. , A melt-dispersion cooling method, an air suspension coating method, a spray drying method and the like, which are appropriately selected according to the application. Further, a secondary resin film may be provided on the surface of the microcapsules according to the purpose to impart durability, or the surface characteristics may be modified for practical use.

  Here, the mass ratio of the reversible thermochromic composition to the microcapsule wall film satisfies the range of 7: 1 to 1: 1, preferably 6: 1 to 1: 1.

  When the ratio of the reversible thermochromic composition to the wall film is larger than the above range, the thickness of the wall film becomes too thin, and the resistance to pressure and heat tends to decrease, and the ratio of the wall film to the reversible thermochromic composition. Is larger than the above range, the color density at the time of color development and the sharpness tend to be lowered.

  The reversible thermochromic microcapsule pigment has a particle size in the range of 0.1 to 5 μm, preferably 0.1 to 3 μm, and more preferably 0.5 to 3 μm. If the particle diameter of the microcapsule pigment exceeds 5 μm, it may be difficult to obtain dispersion stability, and if the particle diameter is less than 0.1 μm, it may be difficult to exhibit high-density color development. The particle size is measured using Multisizer 4e manufactured by Beckman Coulter KK, and the particle size present is determined from the distribution map.

  The reversible thermochromic microcapsule pigments include an antioxidant, an ultraviolet absorber, an infrared absorber, a dissolution aid, an antiseptic / antifungal agent, a non-thermochromic dye or pigment within a range that does not affect its function. And various other additives can be added.

  In addition, a non-thermochromic dye or pigment is blended in the microcapsule pigment or the ink composition to form a thermochromic image exhibiting a tautomerization from the color (1) to the color (2) by a temperature change. It can be configured to be able to.

  The ink composition according to the present invention may contain additives such as a pH adjuster, a preservative or an antifungal agent as needed.

  Examples of the pH adjuster include inorganic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide, and sodium acetate; and organic basic compounds such as water-soluble amine compounds such as triethanolamine and diethanolamine.

  Examples of preservatives or fungicides include 2-methyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 2-methyl- 4,5-trimethylene-4-isothiazolin-3-one, N- (n-butyl) -1,2-benzisothiazolin-3-one, 2-pyridinethiol-1-oxide sodium, 3-iodo-2-propynylbutyl Examples include sodium carbamate benzoate, benzotriazole and phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6-tetrachloro-4- (methylsulfonyl) pyridine and the like. .

  Examples of the rust preventive include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, and dialkylthiourea. In addition, as the water-soluble resin, an acrylic resin, an alkyd resin, polyvinylpyrrolidone, polyvinyl alcohol, or the like can be used. Further, as a resin emulsion, an emulsion containing an acrylic resin, a urethane resin, a styrene-butadiene resin, a polyester resin, a vinyl acetate resin, or the like can be added.

  Further, a fluorine-based surfactant for improving the permeability of the solvent, a nonionic, anionic or cationic surfactant, and an antifoaming agent such as dimethylpolysiloxane can also be added.

  The ink composition has an ink viscosity of preferably 1 to 20 mPa · s, more preferably 5 to 10 mPa · s, measured at 20 ° C. using an EL viscometer at 20 rpm. The ink composition of the present invention exerts its maximum effect when used for a low-viscosity ink.

  The ink composition according to the present invention can be used as a water-based ink for various writing instruments such as a fountain pen, a ballpoint pen, a brush pen, a pen for calligraphy, and various markers. In particular, writing implements having an ink supply mechanism utilizing capillary action, such as writing implements having an ink supply mechanism using a comb groove such as a fountain pen, and ink supply mechanisms using a fiber bundle represented by markers, etc. Because of the ink supply mechanism, it is necessary to use a low-viscosity ink because high-viscosity inks cannot be used.In the conventional aqueous ink composition for writing implements, In some cases, the handwriting is blurred or writing becomes impossible. However, the ink composition according to the present invention is preferably used even in a low-viscosity ink because the microcapsule pigment can be uniformly dispersed.

  The ink composition according to the present invention can be provided in various writing instruments as described above, and it is possible to form a handwriting using the writing instrument, and the handwriting is applied by rubbing with a finger or application of a heating tool or a cooling tool. Can be discolored.

  Examples of the heating tool include an energization heating discoloration tool equipped with a resistance heating element, a heating discoloration tool filled with hot water, and the application of a hair dryer, but preferably, a friction member is used as a means capable of discoloring by a simple method. Can be In particular, an elastic body that does not substantially wear when rubbed is preferable.

  As the friction member, an elastic body such as an elastomer or a plastic foam, which is rich in elasticity and can generate appropriate friction when rubbing and generate frictional heat, is suitable. As the material of the friction member, silicone resin, SEBS resin (styrene-ethylene-butylene-styrene block copolymer), polyester-based resin, polyester-based elastomer and the like are used. The friction member can be a writing instrument set obtained by combining a writing instrument with a friction element that is a member having a different shape, but providing the writing instrument with a friction member provides excellent portability.

  Examples of the cooler include a cooler / discolorer using a Peltier element, a cooler / discolorer filled with a refrigerant such as cold water or ice chips, a cold insulator, and application of a refrigerator or a freezer.

  The thermochromic handwriting can be discolored by applying a heating discoloration device or a cooling discoloration device. Examples of the heating discoloration device include a heating discoloration device equipped with a resistance heating element such as a PTC element, a heating discoloration device filled with a medium such as hot water, a heating discoloration device using steam or laser light, and application of a hair dryer. Preferably, an electric heating and heating discoloring tool is used. Examples of the energizing heat discoloring device include an energizing heating discoloring device using a thermal head, a heat roller, and a hot stamp.

(Writing implement)
The water-based ink composition of the present invention can be used for a writing instrument such as a marking pen or a ballpoint pen having a pen tip such as a fiber tip, a felt tip and a plastic tip or a ballpoint pen tip as a writing tip, and a fountain pen using a metal writing tip. Can be. Among them, when used in a writing implement having a pen tip made of a fiber tip or a felt tip, the dry-up resistance at the tip end is improved, so that the writing performance is improved, and the effect is particularly enhanced. Further, the porosity of the chip is preferably 50 to 80%. When the porosity of the chip falls within the above numerical range, the pigment is not clogged, and an appropriate ink ejection amount can be maintained.

  The writing implement of the present invention may have a configuration in which the aqueous ink composition is directly filled, or may have an ink container or an ink storage body in which the aqueous ink composition can be filled.

  The retracting mechanism of the writing instrument of the present invention is not particularly limited, and examples thereof include a cap type having a cap for covering the pen tip, a knock type, a rotary type, and a slide type. In addition, a retractable type in which a pen point can be accommodated in a shaft cylinder may be used.

  Also, the ink supply mechanism in the writing implement is not particularly limited. For example, (1) a mechanism for supplying an aqueous ink composition to a pen tip by providing an ink guide core made of a fiber bundle or the like as an ink flow rate adjusting member; (2) a mechanism for supplying a water-based ink composition to a pen tip with a comb groove-shaped ink flow rate adjusting member interposed therebetween; A mechanism for supplying the aqueous ink composition directly to the pen tip from the ink container or the barrel having the pen tip.

  In one embodiment, the writing instrument is a marking pen, and the pen tip is not particularly limited, and may be, for example, a fiber tip, a felt tip, a plastic tip, or the like, and further, the shape thereof may be a bullet type, a chisel type or It may be a brush pen type or the like.

  In one embodiment, the writing implement is a ballpoint pen, and in another embodiment, a fountain pen.

  The present invention will be described below using examples.

(Production of microcapsule pigment A)
4.5 parts by mass of 2- (2-chloroanilino) -6-di-n-butylaminofluoran as the component (a) and 2,2-bis (4'-hydroxyphenyl) hexafluoropropane 5 as the component (b) 2.0 parts by mass, 3.0 parts by mass of 4,4 '-(1-methylpentylidene) bisphenol, and 50.0 parts by mass of 4-benzyloxyphenylethyl caprate as a component (c). The thermochromic composition was heated and dissolved, and a solution obtained by mixing 25.0 parts by mass of an aromatic isocyanate prepolymer as a wall film material and 50.0 parts by mass of a cosolvent was emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution. After stirring while heating, 2.5 parts by mass of a water-soluble aliphatic modified amine was added, and stirring was further continued to obtain a reversible thermochromic microcapsule pigment suspension. The suspension was centrifuged to isolate the reversible thermochromic microcapsule pigment A.
When the particle diameter of the microcapsule pigment A was measured using a Multisizer 4e (manufactured by Beckman Coulter, Inc.), it was in the range of 0.5 to 5.0 μm. The color development temperature is −10 ° C., and the color reversibly changes from black to colorless and from colorless to black by a change in temperature.

(Production of microcapsule pigment B)
Microcapsule pigment B was obtained in the same manner as microcapsule pigment A, except that component (a), component (b), and component (c) were as described below.
2.0 parts by mass of 3- (4-diethylamino-2-hexyloxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide as the component (a) 8.0 parts by mass of 2,2-bis (4'-hydroxyphenyl) hexafluoropropane (c) 40.0 parts by mass of 4-benzyloxyphenylethyl caprate as a component The particle diameter of the microcapsule pigment B is Multisizer 4e When measured using Beckman Coulter Co., Ltd., it was in the range of 0.5 to 5.0 μm, the complete decoloration temperature was 60 ° C., the complete color development temperature was −10 ° C., and the temperature changed from blue to blue. Colorless, reversibly changes color from colorless to blue.

(Production of microcapsule pigment C)
4.0 parts by mass of 4- [2,6-bis (2-ethoxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine as a component (b) 2,2-bis (4 'as a component (Hydroxyphenyl) hexafluoropropane 8.0 parts by mass (c) A reversible thermochromic composition having a color memory consisting of 40.0 parts by mass of 4-benzyloxyphenylethyl caprate as a component is heated and dissolved. A solution obtained by mixing 30.0 parts by mass of an aromatic isocyanate prepolymer and 40.0 parts by mass of a cosolvent as a film material is emulsified and dispersed in an 8% aqueous solution of polyvinyl alcohol, and the mixture is stirred while heating, and then dissolved in water. 2.5 parts by mass of an aliphatic modified amine was added, and stirring was further continued to obtain a reversible thermochromic microcapsule pigment suspension. The suspension was centrifuged to isolate the reversible thermochromic microcapsule pigment C. The particle size of the microcapsule pigment C was measured using a Multisizer 4e (manufactured by Beckman Coulter, Inc.), and was in the range of 0.5 to 4.0 μm. The temperature was −10 ° C., and the color changed reversibly from yellow to colorless and from colorless to yellow due to the temperature change.

(Production of microcapsule pigment D)
Microcapsule pigment D was obtained in the same manner as microcapsule pigment C, except that component (a), component (b), and component (c) were as described below.
(I) 2- (dibutylamino) -8- (dipentylamino) -4-methyl-spiro [5H- [1] benzopyrano [2,3-g] pyrimidine-5,1 '(3'H)- Isobenzofuran] -3-one 2.5 parts by mass (b) 2,2-bis (4'-hydroxyphenyl) hexafluoropropane 5.0 parts by mass as a component, 4,4 '-(1-methylpentylidene) 3.0 parts by mass of bisphenol (c) 50.0 parts by mass of 4-benzyloxyphenylethyl caprate as a component The particle diameter of the microcapsule pigment D was measured using a Multisizer 4e (manufactured by Beckman Coulter, Inc.). However, it is in the range of 0.5 to 4.0 μm, the complete color erasing temperature is 60 ° C., and the complete color developing temperature is −10 ° C. Was reversibly color change to pink.

  The microcapsule pigments A to D had different specific gravities, and the relationship was microcapsule pigment A> microcapsule pigment B> microcapsule pigment C> microcapsule pigment D.

(Example 1)
(Production of water-based ink composition for reversible thermochromic writing implement)
Reversible thermochromic microcapsule pigment A 18.0 parts by mass Reversible thermochromic microcapsule pigment D 2.0 parts by mass Sodium chloride (inorganic salt of monovalent cation) 6.1 parts by mass Glycerin 25.0 parts by mass MPC Polymer 1.0 part by mass Water 47.9 parts by mass The above composition was stirred and mixed by a homodisper manufactured by PRIMIX to obtain a reversible thermochromic aqueous ink composition.
The viscosity of the ink composition was 9 mPa · s.
When the behavior of the microcapsule pigments A and D in a vehicle not containing the MPC polymer was confirmed, the microcapsule pigment A settled and the microcapsule pigment D floated.

(Examples 2 to 14, Comparative Examples 1 to 6)
The ink compositions of Examples 2 to 14 and Comparative Examples 1 to 6 were obtained by changing the types and the amounts of the components to be blended in Example 1 as shown in Tables 1 and 2. Details of the materials used in these examples are as follows.
Also, as in Example 1, the results of confirming the behavior of the microcapsule pigment in a vehicle containing no MPC polymer are also shown.

（１）黒色マイクロカプセル顔料
（２）青色マイクロカプセル顔料
（３）黄色マイクロカプセル顔料
（４）桃色マイクロカプセル顔料
（５）２−メタクリロイルオキシエチルホスホリルコリンを構成単位に含むポリマー４０％水溶液、日油（株）製、商品名：ＬＩＰＩＰＵＲＥ−ＨＭ
（６）２−メタクリロイルオキシエチルホスホリルコリンを構成単位に含むポリマーと２−メタクリロイルオキシブチルを構成単位に含むポリマーとの共重合体５％水溶液、日油（株）製、商品名：ＬＩＰＩＰＵＲＥ−ＰＭＢ
（７）２−メタクリロイルオキシエチルホスホリルコリンを構成単位に含むポリマーと２−メタクリロイルオキシブチルを構成単位に含むポリマーと２−メタクリル酸ナトリウムを構成単位に含むポリマーとの共重合体５％水溶液、日油（株）製、商品名：ＬＩＰＩＰＵＲＥ−Ａ
（８）ダイセルファインケム（株）製、商品名：ＨＥＣダイセルＳＰ２００

(1) Black microcapsule pigment (2) Blue microcapsule pigment (3) Yellow microcapsule pigment (4) Pink microcapsule pigment (5) 40% aqueous solution of polymer containing 2-methacryloyloxyethyl phosphorylcholine in a structural unit, NOF ( Co., Ltd., trade name: LIPIPURE-HM
(6) 5% aqueous solution of a copolymer of a polymer containing 2-methacryloyloxyethylphosphorylcholine in a constituent unit and a polymer containing 2-methacryloyloxybutyl in a constituent unit, manufactured by NOF Corporation, trade name: LIPIPURE-PMB
(7) A 5% aqueous solution of a copolymer of a polymer containing 2-methacryloyloxyethyl phosphorylcholine in a constitutional unit, a polymer containing 2-methacryloyloxybutyl in a constitutional unit and a polymer containing sodium 2-methacrylate in a constitutional unit, NOF Product name: LIPIPURE-A
(8) Daicel Finechem Co., Ltd., trade name: HEC Daicel SP200

  The ink compositions obtained in Examples 1 to 14 and Comparative Examples 1 to 6 were evaluated as follows. Table 2 shows the results.

（マイクロカプセル顔料分散安定性試験）
（株）パイロットコーポレーション製ペチット１インキカートリッジに実施例１〜１４、比較例１〜６のインキ組成物を充填して栓をし、縦方向に保管し、２５℃にて４週間静置後の外観を確認した。
○：初期同等に均一に分散しており、明確な変化はみられない。
△：初期、顔料がわずかに沈降し、上澄みがみられたが、初期とほとんど変化はみられない。
×：顔料が沈降または浮遊し、インキ組成物が明らかに分離しており、初期よりも沈降または浮遊が進行している。

(Microcapsule pigment dispersion stability test)
After filling the ink compositions of Examples 1 to 14 and Comparative Examples 1 to 6 into a petite 1 ink cartridge manufactured by Pilot Corporation, stoppering, storing the ink composition in the vertical direction, and allowing it to stand at 25 ° C. for 4 weeks. The appearance was confirmed.
：: uniformly dispersed in the initial stage, and no clear change is observed.
Δ: At the initial stage, the pigment slightly settled and the supernatant was observed, but almost no change was observed from the initial stage.
X: The pigment sediments or floats, the ink composition is clearly separated, and the sedimentation or floating progresses from the initial stage.

(Written test)
Using a petite 1 manufactured by Pilot Corporation as a direct liquid type marker and friction colors as a filling type marker, inks of Examples 1 to 14 and Comparative Examples 1 to 6 were accommodated to prepare a writing instrument. Was stored with the chip facing upward and downward, and allowed to stand at room temperature for 4 weeks, followed by writing and evaluation.
：: Writing is possible from the first stroke, and there is no difference in shading of the handwriting depending on the tip direction.
Δ: Writing is possible from the first stroke, but the handwriting density difference is remarkable depending on the tip direction.
×: Cannot be written.

(Handwriting dryness)
Writing was performed on paper A in the running test using a filled marker, and after one minute, the handwriting was erased and rubbed with a rubber, and the state was confirmed by visual observation.
：: Handwriting is dry and no stain is generated.
×: There is an undried part in the handwriting, and stain is generated.

  As is clear from the results in Table 3, the ink compositions of Examples 1 to 14 were excellent in the dispersion stability of the microcapsule pigment, and were excellent in writing properties and handwriting drying property even when used in a writing instrument. . On the other hand, in the ink composition of Comparative Example 1, those in which the microcapsule pigment was floating and those in which the microcapsule pigment was settled were observed. In the ink compositions of Comparative Examples 2 and 3, the microcapsule pigment was settled. In each case, the dispersion stability of the microcapsule pigment was inferior and was not suitable as an aqueous ink composition for writing implements. The ink compositions of Comparative Examples 4 and 5 were excellent in dispersion stability, however, in Comparative Example 4, the handwriting drying property was particularly poor. Sodium was precipitated and the writability was poor, and all of them had poor performance when used for a writing instrument. In the ink composition of Comparative Example 6, the microcapsule pigment formed a loose aggregate with hydroxyethyl cellulose, and the aggregate was settled, but the dispersion state was stable. However, when used in a writing instrument, the effect of sedimentation was observed, and the writing properties were poor.

  The reversible thermochromic water-based ink composition according to the present invention can be used as a water-based ink for various writing instruments such as a fountain pen, a ballpoint pen, a brush pen, a pen for calligraphy, and various markers. In particular, it can be suitably used for a writing instrument using a low-viscosity ink.

t ₁ heating color development initiation temperature t ₃ heating consumption microcapsule pigment enclosing a decolorizable the complete coloring temperature t ₂ heated decolorizable reversible thermochromic composition of the microcapsule pigment enclosing a reversible thermochromic composition complete decoloring temperature ΔH hysteresis width of the microcapsule pigment enclosing a color type decoloring starting temperature t ₄ heated decolorizable reversible thermochromic composition of the microcapsule pigment enclosing a reversible thermochromic composition

Claims (6)

(B) a component comprising an electron-donating color-forming organic compound;
(B) a component comprising an electron-accepting compound;
(C) a reaction medium that reversibly causes an electron transfer reaction by the components (a) and (b) in a specific temperature range;
A reversible thermochromic microcapsule pigment containing a reversible thermochromic composition comprising:
A polymer containing 2-methacryloyloxyethyl phosphorylcholine in a structural unit,
A reversible thermochromic pigment comprising glycerin, a monovalent inorganic salt of a cation, and water, wherein the reversible thermochromic microcapsule pigment comprises two or more microcapsule pigments having different specific gravities. A water-based ink composition for writing implements.   The composition according to claim 1, wherein the content of the inorganic salt of the monovalent cation is 1 to 10% by mass based on the total mass of the aqueous ink composition.   The composition according to claim 1, wherein the content of the glycerin is larger than the content of the inorganic salt of a monovalent cation on a mass basis.   The composition according to any one of claims 1 to 3, wherein the inorganic salt of a monovalent cation is an alkali metal salt.   The composition according to any one of claims 1 to 4, wherein a viscosity measured by an EL viscometer at a rotation speed of 20 rpm and 20 ° C is 1 to 20 mPa · s.   A writing instrument comprising the composition according to any one of claims 1 to 5.

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