JP5754966B2 - Water-based ink composition for writing instruments - Google Patents

Description

  The present invention relates to a water-based ink composition for a writing instrument using a thermochromic colorant utilizing the color developing and decoloring mechanism of a leuco dye. More specifically, the average particle size is small, and the content in the ink The present invention relates to a water-based ink composition for a writing instrument that can provide a satisfactory drawn line density even when the amount of the ink is reduced.

  Conventionally, a water-based ink composition for a writing instrument using a thermochromic colorant utilizing a leuco dye developing and decoloring mechanism usually uses a pigment in which the above compound is microencapsulated.

For example, (a) an electron-donating color-forming organic compound that is a leuco dye, (b) an electron-accepting compound that is a developer, and (c) a color-change temperature adjusting agent that determines the temperature at which the color reaction occurs. As a reaction medium, a temperature-sensitive color-changing color memory ink composition for a writing instrument (for example, a thermo-sensitive color-changing color memory composition containing a temperature-sensitive color-changing color memory composition comprising a homogeneous solution of a specific ester compound and a solvent) In the paragraph [0007] of the document 1, as the leuco dye, known diphenylmethane phthalides, phenyl indolyl phthalides, indolyl phthalides, diphenylmethane aza are used. Examples include phthalides, phenylindolylazaphthalides, fluorans, styrinoquinolines, diazarhodamine lactones, and the like.
However, the water-based ink composition for writing instruments using the microcapsule pigment as the conventional thermochromic colorant including the above-mentioned Patent Document 1 originally has a poor leuco color, and the wall film of the microcapsule has a drawn line density. It is the cause that has lowered.

In order to increase the line density, it is conceivable to increase the content of the microcapsule pigment in the ink or to increase the average particle size of the microcapsule pigment.
However, in the former case, the writing feeling is remarkably lowered, and in the latter case, there are problems such as deterioration of ink discharge property and microcapsule pigment settling over time.

JP-A-2005-213361 (Claims, Examples, etc.)

  The present invention is to solve this problem in view of the above-mentioned problems of the prior art and the present situation. The average particle size is small, and even if the microcapsule pigment content in the ink is reduced, it is satisfactory and sufficient. An object of the present invention is to provide a water-based ink composition for a writing instrument that provides a drawn line density.

  As a result of intensive studies in view of the above-described conventional problems, the present inventor has found that a water-based ink composition for a writing instrument can be obtained by using a microcapsule pigment using a specific leuco dye. The present invention has been completed.

（２） 前記顕色剤が下記式（II）で示されることを特徴とする上記（１）に記載の筆記具用水性インク組成物。

〔上記式（II）中のＲ１は、水素原子又は炭素数１〜２のアルキル基を示し、Ｒ２は、炭素数４〜１０の直鎖又は分岐のアルキル基を示す。〕
（３） 前記変色温度調整剤が下記式（III）で示されることを特徴とする上記（１）又は（２）に記載の筆記具用水性インク組成物。

〔上記式（III）中のＲ３及びＲ４は、炭素数７〜２１の直鎖又は分岐のアルキル基を示し、Ｒ５及びＲ６は、水素原子、炭素数１〜２のアルキル基、又はＣＦ_３を示す。〕
（４） 前記マイクロカプセル顔料を構成する壁膜がメラミン樹脂である上記（１）〜（３）の何れか一つに記載の筆記具用水性インク組成物。
（５） 前記マイクロカプセル顔料の平均粒子径が０．３〜１．０μｍであることを特徴とする上記（１）〜（４）の何れか一つに記載の筆記具用水性インク組成物。 That is, the present invention resides in the following (1) to (5).
(1) A water-based ink composition for a writing instrument comprising a microcapsule pigment containing at least a leuco dye represented by the following formula (I), a developer, and a color change temperature adjusting agent.

(2) The aqueous ink composition for a writing instrument as described in (1) above, wherein the developer is represented by the following formula (II).

[R1 in the above formula (II) represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R2 represents a linear or branched alkyl group having 4 to 10 carbon atoms. ]
(3) The aqueous ink composition for a writing instrument as described in (1) or (2) above, wherein the discoloration temperature adjusting agent is represented by the following formula (III).

[R3 and R4 in the above formula (III) represent a linear or branched alkyl group having 7 to 21 carbon atoms, and R5 and R6 represent a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, or CF ₃ . Show. ]
(4) The water-based ink composition for a writing instrument according to any one of (1) to (3), wherein the wall film constituting the microcapsule pigment is a melamine resin.
(5) The water-based ink composition for a writing instrument as described in any one of (1) to (4) above, wherein the microcapsule pigment has an average particle size of 0.3 to 1.0 μm.

  According to the present invention, there is provided an aqueous ink composition for a writing instrument that has a small average particle diameter and that can provide a satisfactory sufficient line density even when the content in the ink is reduced.

用いるマイクロカプセル顔料は、上記式（Ｉ）で示されるロイコ色素、顕色剤、変色温度調整剤から少なくとも構成される熱変色性組成物を内包させたものである。 Hereinafter, embodiments of the present invention will be described in detail.
The aqueous ink composition for a writing instrument of the present invention comprises a microcapsule pigment containing at least a leuco dye represented by the following formula (I), a developer and a color change temperature adjusting agent.

The microcapsule pigment to be used encapsulates a thermochromic composition comprising at least a leuco dye represented by the above formula (I), a developer, and a color change temperature adjusting agent.

<Leuco dye>
The leuco dye represented by the above formula (I) used in the present invention is a compound [3-di (n-butyl) amino-6-methoxy-7 which has excellent color development properties as a black leuco dye and has a clear black color tone. -Anilinofluorane].
Generally, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane is known as a black leuco dye. In the present invention, the leuco dye represented by the above formula (I) is used. By using a microcapsule pigment using, the average particle size is small, and even if the content in the ink is reduced, a satisfactory drawn line density can be obtained.

〔式（II）中のＲ１は水素原子又は炭素数１〜２のアルキル基を示し、Ｒ２は炭素数４〜１０の直鎖又は分岐のアルキル基を示す。〕 <Developer>
The developer used in the present invention is a component having the ability to develop the leuco dye represented by the above formula (I). As the developer to be used, conventionally known developers can be used, and examples thereof include inorganic acids, aromatic carboxylic acids and anhydrides or metal salts thereof, organic sulfonic acids, other organic acids, and phenolic compounds. .
Preferably, it is a bisphenol derivative, and what is shown by the compound of following formula (II) is mentioned.

[R1 in Formula (II) represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R2 represents a linear or branched alkyl group having 4 to 10 carbon atoms. ]

  Specific examples of the compound of the formula (II) include 4,4 ′-(2-ethylhexylidene) bisphenol, 4,4 ′-(2-ethylpentylidene) bisphenol, and 4,4′-octyl. Ridenbisphenol, 4,4'-hexylidenebisphenol, 4,4 '-(4-methyloctylidene) bisphenol, 4,4'-decylidenebisphenol, 4,4'-(1,3-dimethylbutylidene) Bisphenol, 4,4 '-(3-methylbutylidene) bisphenol, 4,4'-(1-methylbutylidene) bisphenol, 4,4 '-(1,2-dimethylbutylidene) bisphenol, 4,4 '-(1,5-dimethylhexylidene) bisphenol, 4,4'-(1-ethyl-3-methylpentylidene) bisphenol, 4,4 '-(1-methyl) -4-methylheptylidene) bisphenol, 4,4 '-(1-ethyl-hexylidene) bisphenol, 4,4'-(1-ethyl-pentylidene) bisphenol, 4,4 '-(1-ethyl-octylidene) Although at least 1 type (each single or 2 or more types of mixtures, and the following similarly), such as bisphenol, can be mentioned, Of course, it is not limited to these.

  In the present invention, one or two or more of these developers are used in combination, or a conventionally known developer is used in combination within a range that does not impair the properties of the developer of the present invention. Thus, the color density at the time of color development can be freely adjusted. Accordingly, the amount used may be arbitrarily selected according to the desired color density, and is not particularly limited, but is usually 0.1 to 100 mass with respect to 1 part by mass of the leuco dye described above. It is preferable to select within the range of about parts.

〔式（III）中のＲ３及びＲ４は、直鎖又は分岐の炭素数７〜２１のアルキル基を示し、Ｒ５及びＲ６は、水素原子、炭素数１〜２のアルキル基、又はＣＦ３を示す。〕 <Discoloration temperature regulator>
The color change temperature adjusting agent used in the present invention is a substance that controls the color change temperature in the coloration of the leuco dye and the developer.
Conventionally known color change temperature adjusting agents can be used. Specific examples include alcohols, esters, ketones, ethers, acid amides, azomethines, fatty acids, hydrocarbons and the like.
Preferably, it is an ester compound composed of a bisphenol derivative and a saturated fatty acid having 8 to 22 carbon atoms, and is represented by a compound of the following formula (III).

[R3 and R4 in Formula (III) represent a linear or branched alkyl group having 7 to 21 carbon atoms, and R5 and R6 represent a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, or CF3. ]

  Specific examples of the compound of the formula (III) include 4,4 ′-(hexafluoroisopropylidene) bisphenol dicaprate, 4,4 ′-(hexafluoroisopropylidene) bisphenol dilaurate, 4,4 ′-( Hexafluoroisopropylidene) bisphenol dimyristate, 4,4 ′-(hexafluoroisopropylidene) bisphenol dipalmiate, 4,4 ′-(hexafluoroisopropylidene) bisphenol diundecanoate, 4,4 ′-(hexa) Fluoroisopropylidene) bisphenol ditridecate, 4,4 ′-(isopropylidene) bisphenol dicaprate, 4,4 ′-(isopropylidene) bisphenol dilaurate, 4,4 ′-(isopropylidene) bisphenol dimyristate, 4 4 '-(isopropylidene) bisphenol dipalmiate, 4,4'-(isopropylidene) bisphenol diundecanoate, 4,4 '-(isopropylidene) bisphenol ditridecanate, 4,4'-methylene bisphenol dicaprate 4,4'-methylene bisphenol dilaurate, 4,4'-methylene bisphenol dimyristate, 4,4'-methylene bisphenol dipalmitate, 4,4'-methylene bisphenol diundecanoate, 4,4'-methylene There may be mentioned at least one kind such as bisphenol ditridecate.

The amount of the color-change temperature adjusting agent used may be appropriately selected according to the desired hysteresis width and color density at the time of color development, and is not particularly limited, but is usually based on 1 part by mass of the leuco dye. , Preferably in the range of about 1 to 1000 parts by mass.
In addition, if it is in the range which does not impair the various characteristics of the composition of this invention, a conventionally well-known discoloration temperature regulator can also be used in combination.

<Microcapsule pigment>
The microcapsule pigment used in the present invention is a thermochromic composition comprising at least the leuco dye, a developer, and a color change temperature adjusting agent, and preferably has an average particle size of 0.3 to 1.0 μm. It can be produced by microencapsulation.
Examples of the microencapsulation method include interfacial polymerization method, interfacial polycondensation method, in situ polymerization method, liquid curing coating method, phase separation method from aqueous solution, phase separation method from organic solvent, melt dispersion cooling method, air A suspension coating method, a spray drying method, etc. can be mentioned, and can be appropriately selected according to the application.

  For example, in a phase separation method from an aqueous solution, a leuco dye, a developer, and a color change temperature adjusting agent are heated and melted, then charged into an emulsifier solution, heated and stirred to disperse into oil droplets, and then as a capsule film agent, Use resin raw materials, for example, amino resin solution, specifically, each solution such as methylol melamine aqueous solution, urea solution, benzoguanamine solution, etc., gradually add and continue to react, then filter this dispersion Thus, the desired thermochromic microcapsule pigment can be produced.

The content of these leuco dyes, developer, and color change temperature adjusting agent varies depending on the type of leuco dye, developer, color change temperature adjusting agent used, microencapsulation method, etc. The ratio is 0.1 to 100 developer and 1 to 100 color changing temperature adjusting agent. Moreover, a capsule membrane agent is 0.1-1 by mass ratio with respect to the capsule content.
In the microcapsule pigment of the present invention, the black coloring temperature and decoloring temperature can be set to suitable temperatures by suitably combining the types and amounts of the leuco dye, the developer and the color change temperature adjusting agent. .

In the microcapsule pigment of the present invention, the wall film is preferably formed of an amino resin from the viewpoint of further improving the line density, storage stability, and writing property, for example, melamine resin, urea resin, benzoguanamine resin, etc. It is desirable to form with a melamine resin from the viewpoint of manufacturing, storage stability, and writing property.
The thickness of the wall film of the microcapsule pigment is appropriately determined according to the required strength of the wall film and the drawn line density.
In order to form the wall film with an amino resin, when using each microencapsulation method, a suitable amino resin raw material (melamine resin, urea resin, benzoguanamine resin, etc.), dispersant, protective colloid Select etc.

The average particle size of the microcapsule pigment used in the present invention is preferably 0.3 to 1 from the viewpoints of colorability, color developability, easy decolorization, stability, and the adverse effect on writing properties. A thickness of 0.0 μm is desirable. The “average particle size” defined in the present invention (including examples and the like) is a value obtained by measuring the average particle size with a particle size distribution measuring device [particle size measuring instrument N4Plus (manufactured by COULTER)].
If the average particle diameter is less than 0.3 μm, sufficient line density cannot be obtained. On the other hand, if it exceeds 1.0 μm, the writability is deteriorated and the dispersion stability of the microcapsule pigment is decreased. Absent.
The microcapsule pigment having the above average particle diameter range (0.3 to 1.0 μm) varies depending on the microencapsulation method. However, in the phase separation method from an aqueous solution, the microcapsule pigment is produced. It can be prepared by suitably combining stirring conditions.

In the present invention, the content of the microcapsule pigment is preferably 5 to 30% by mass (hereinafter simply referred to as “%”), more preferably 10 to 25% with respect to the total amount of the ink composition. desirable.
When the content of the microcapsule pigment is less than 5%, coloring power and color developability are insufficient. On the other hand, when the content exceeds 30%, blurring tends to occur, which is not preferable.

  In the aqueous ink composition for a writing instrument of the present invention, in addition to the microcapsule pigment, the balance is water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as a solvent, and each writing instrument (ballpoint pen). Depending on the purpose of use, for marking pens, etc., water-soluble organic solvents, thickeners, lubricants, rust preventives, antiseptics or antibacterial agents are appropriately contained within the range not impairing the effects of the present invention. be able to.

  Examples of water-soluble organic solvents that can be used include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, and glycerin, ethylene glycol monomethyl ether, and diethylene glycol monomethyl. Ethers can be used alone or in combination.

  As the thickener that can be used, for example, at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides is desirable. Specifically, gum arabic, gum tragacanth, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutane gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid and Salts thereof, propylene glycol alginate, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylic acid and salts thereof, carboxyvinyl polymer, polyethylene oxide, copolymer of vinyl acetate and polyvinyl pyrrolidone, cross-linked acrylic acid polymer and Examples thereof include non-crosslinked acrylic acid polymers and salts thereof, styrene acrylic acid copolymers and salts thereof, and the like. That.

  Lubricants include nonionics such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphates, which are also used in pigment surface treatment agents, and alkyl sulfonic acids of higher fatty acid amides. Examples thereof include salts, anionic compounds such as alkyl allyl sulfonates, polyalkylene glycol derivatives, fluorosurfactants, and polyether-modified silicones. In addition, as rust preventives, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, etc., as antiseptics or fungicides, phenol, sodium omadin, sodium benzoate, benzimidazole compounds, etc. Can be mentioned.

  In order to produce the aqueous ink composition for a writing instrument of the present invention, a conventionally known method can be employed. For example, in addition to the microcapsule pigment, a predetermined amount of each of the above components is blended, and a homomixer, or It is obtained by stirring and mixing with a stirrer such as a disper. Furthermore, if necessary, coarse particles in the ink composition may be removed by filtration or centrifugation.

  In the aqueous ink composition for a writing instrument of the present invention thus configured, an ink containing a microcapsule pigment containing at least a leuco dye represented by the above formula (I), a developer and a color change temperature adjusting agent is formulated, Even when writing on paper or the like with a writing instrument such as a ballpoint pen or marking pen equipped with this ink, the average particle diameter is small, and even if the content in the ink is reduced, a satisfactory line density is satisfactory. The obtained water-based ink composition for writing instruments is obtained.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to the following Example etc. In the following, “part” as a blending unit means part by mass.

[Examples 1-7 and Comparative Examples 1-2]
(Microcapsule pigment: formulation of A-1 to A-9)
(Microcapsule pigment: A-1)
As a leuco dye, 1 part of the compound represented by the above chemical formula 1, as a developer, 2,4 '-(2-ethylhexylidene) bisphenol, and as a color-changing temperature adjusting agent, 4,4'-( 24 parts of hexafluoroisopropylidene) bisphenol dimyristate were heated and melted to 100 ° C. to obtain 27 parts of a homogeneous composition.
Using a uniform hot solution of 27 parts of the composition obtained above as a protective colloid agent, 40 parts of methyl vinyl ether / maleic anhydride copolymer resin (Gantretz AN-179: manufactured by ISP Co., Ltd.) was adjusted to pH 4 with NaOH. While gradually adding to 100 parts of the dissolved 90 ° C. aqueous solution, the mixture is heated and stirred to disperse into oil droplets having a diameter of about 0.5 to 1.0 μm, and then as a capsule film agent, melamine resin (Sumitex resin) M-3 (manufactured by Sumitomo Chemical Co., Ltd.) is gradually added, and heated to 90 ° C. for 30 minutes for microencapsulation, and the film agent is a micro of reversible thermochromic hysteresis composition comprising a melamine resin. A capsule solution was obtained. When the particle diameter of this solution was measured, the average particle diameter was 0.74 μm, and it contained 32% of particles of 0.5 μm or less. The hue was dark black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-2)
In the above formula A-1, except that 4,4′-isopropylidenebisphenol dimyristate is used as the color change temperature adjusting agent instead of 4,4 ′-(hexafluoroisopropylidene) bisphenol dimyristate, Other than that, the microcapsule solution of the reversible thermochromic hysterin composition containing 34% of particles having an average particle diameter of 0.69 μm and 0.5 μm or less was obtained in the same manner as the formulation of A-1. The hue was dark black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-3)
In the prescription of A-1, in the place of 4,4 '-(2-ethylhexylidene) bisphenol as a developer, 4,4'-(1,3-dimethylbutylidene) bisphenol is used, In addition, except that 4,4′-isopropylidenebiphenol dilaurate is used in place of 4,4 ′-(hexafluoroisopropylidene) bisphenol dimyristate as the color change temperature adjusting agent, the other is the formulation of A-1 above In the same manner as above, a microcapsule solution of a reversible thermochromic hysteresis composition containing 28% of particles having an average particle size of 0.78 μm and 0.5 μm or less was obtained. The hue was dark black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-4)
In the formula A-2, 4,4 ′-(1,3-dimethylbutylidene) bisphenol is used as a developer instead of 4,4 ′-(2-ethylhexylidene) bisphenol. Except for the above, a microcapsule solution of a reversible thermochromic hysteresis composition containing 32% of particles having an average particle size of 0.74 μm and 0.5 μm or less was obtained in the same manner as in A-2 above. The hue was dark black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-5)
In the above formula A-1, except that 4,4′-ethylidenebisphenol dilaurate is used instead of 4,4 ′-(hexafluoroisopropylidene) bisphenol dimyristate as the color changing temperature adjusting agent In the same manner as the formulation of A-1, a reversible thermochromic hysterin composition containing 33% of particles having an average particle size of 0.73 μm and 0.5 μm or less was obtained. The hue was dark black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-6)
In the above formula A-1, 4,4 '-(1-methylpropylidene) bisphenol dilaurate should be used as the color change temperature adjusting agent instead of 4,4'-(hexafluoroisopropylidene) bisphenol dimyristate. The microcapsule solution of the reversible thermochromic hysteresis composition containing 31% of particles having an average particle size of 0.78 μm and 0.5 μm or less was obtained in the same manner as in the formulation of A-1 above. The hue was dark black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-7)
In the above formula A-1, 4,4 '-(1-ethylpropylidene) bisphenol dilaurate is used in place of 4,4'-(hexafluoroisopropylidene) bisphenol dimyristate as a color change temperature adjusting agent. The microcapsule solution of the reversible thermochromic hysteresis composition containing 32% of particles having an average particle diameter of 0.75 μm and 0.5 μm or less was obtained in the same manner as in A-1 above. The hue was dark black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-8)
The formulation of A-1, except that 3-dibutylamino-6-methyl-7-anilinofluorane is used as the leuco dye in place of the compound of Chemical Formula 1 as the leuco dye. In the same manner as described above, a microcapsule solution of a reversible thermochromic hysterin composition containing 29% of particles having an average particle diameter of 0.72 μm and 0.5 μm or less was obtained. The hue was black in the colored state and completely colorless with no residual color in the decolored state.

(Microcapsule pigment: A-9)
In the formulation of A-1, except that 2- (2-chloroanilino) -6-di-n-butylaminofluorane is used as the leuco dye in place of the compound of Chemical Formula 1 above, the other A- In the same manner as in No. 1, a microcapsule solution of a reversible thermochromic hysterin composition containing 73% of particles having an average particle size of 0.69 μm and 0.5 μm or less was obtained. The hue was black in the colored state and completely colorless with no residual color in the decolored state.

(Ink formula)
According to the formulation shown in the following Table 1 (microcapsule pigment: A-1 to A-9, thickener, rust preventive, preservative, solvent, water) Prepared. In addition, each microcapsule pigment A-1 to A-9 was taken out and used as a microcapsule pigment by filtering and drying each microcapsule solution.

(Production of water-based ballpoint pen)
A water-based ballpoint pen was produced using each ink composition obtained above. Specifically, a ball pen [Mitsubishi Pencil Co., Ltd., trade name: Signo UM-100] shaft is used, an inner diameter of 3.8 mm, a length of 113 mm, a polypropylene ink containing tube, and a stainless tip (superhard alloy). Each ink is filled in a refill comprising a ball, a ball diameter of 0.5 mm) and a joint connecting the receiving tube and the tip, and an ink follower mainly composed of mineral oil is loaded at the rear end of the ink. Produced.
Using the obtained water-based ballpoint pens of Examples 1 to 7 and Comparative Examples 1 and 2, the drawn line density was evaluated by the following evaluation method.
These results are shown in Table 1 below.

(Drawing line density evaluation method)
Each pen body was spirally written freehand on writing paper compliant with the ISO standard, and then the drawing density was visually evaluated according to the following criteria.
Evaluation criteria:
○: The color is dark black.
Δ: Slightly light density in the colored state.
X: The density is low in a colored state.

As is apparent from the results of Table 1 above, the aqueous ink compositions for writing instruments of Examples 1 to 7 according to the present invention are compared with the aqueous ink compositions for writing instruments of Comparative Examples 1 and 2 that are outside the scope of the present invention. It was found that the line density was satisfactory and satisfactory.
In contrast, an ink composition containing a microcapsule pigment using 3-dibutylamino-6-methyl-7-anilinofluorane as the leuco dye of Comparative Example 1, and 2 as the leuco dye of Comparative Example 2 The ink composition containing the microcapsule pigment using-(2-chloroanilino) -6-di-n-butylaminofluorane cannot obtain a satisfactory sufficient line density.

  A water-based ink composition for a writing instrument suitable for ballpoint pens, marking, etc., which has a small average particle diameter and can provide a satisfactory drawing density even if the content in the ink is reduced.

Claims (5)

A water-based ink composition for a writing instrument, comprising a microcapsule pigment containing at least a leuco dye represented by the following formula (I), a developer, and a color change temperature adjusting agent.

The aqueous ink composition for a writing instrument according to claim 1, wherein the developer is represented by the following formula (II).

[R1 in the above formula (II) represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R2 represents a linear or branched alkyl group having 4 to 10 carbon atoms. ] The water-color ink composition for a writing instrument according to claim 1 or 2, wherein the color-change temperature adjusting agent is represented by the following formula (III).

[R3 and R4 in the above formula (III) represent a linear or branched alkyl group having 7 to 21 carbon atoms, and R5 and R6 represent a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, or CF ₃ . Show. ]   The water-based ink composition for a writing instrument according to any one of claims 1 to 3, wherein the wall film constituting the microcapsule pigment is a melamine resin.   The water-based ink composition for a writing instrument according to any one of claims 1 to 4, wherein the microcapsule pigment has an average particle size of 0.3 to 1.0 µm.