Ink composition for writing instruments

Abstract

Provided is an ink composition for writing instruments having excellent light resistance and storage stability.　This ink composition for writing instruments is characterized by containing at least an azo iron dye represented by (α) below.　(In formula (α), R1 are the same or different and represent a hydrogen atom or an alkyl group having 1-12 carbon atoms; R2 and R3 are the same or different and represent an alkyl group having 3-10 carbon atoms; and A+ represents an ammonium ion of a guanidine derivative or a monovalent ammonium ion that has an alkyl group having 3-18 carbon atoms).

Description

Ink composition for writing instruments

[0001] This specification relates to ink compositions for writing instruments that have high blackness while also exhibiting excellent lightfastness and storage stability.

[0002] Traditionally, in order to create black ink compositions for writing instruments and other applications that provide fastness, primarily lightfastness, using black dyes, it has been necessary to use dyes with a heavy metal complex skeleton. Generally, these complexes have often used heavy metals that are harmful (such as Cr, Co, Cd, Pb, etc., as defined in the European standard: Toy Safety EN71-3:2019 and the International Toy Safety Standard (ISO 8124-3), Part 3 of the International Toy Safety Standard established by the International Organization for Standardization, ISO).

[0003] In current circumstances, it is necessary to address environmental impact and heavy metal regulations in various countries, and there is a demand for the use of dyes that do not contain heavy metals. However, simply dissolving heavy metal-free dyes directly in oily solvents or emulsifying them into inks results in poor lightfastness, insufficient blackness (bluish-black or reddish-black), and poor storage stability.

[0004] On the other hand, conventionally, azo iron dyes of a specific structure, which are oil-soluble black colorants, are known to be free of harmful heavy metals, have sufficient solubility in organic solvents for practical use, and exhibit good black color (see, for example, Patent Documents 1 and 2). On the other hand, as a higher quality oil-based black ink composition that suppresses the bleeding of dyes other than black from handwriting, a black ink composition is known that contains a black dye such as C.I. Solvent Black 7 as the main colorant, and is characterized by comprising an organic solvent consisting of a glycol ether-based solvent or an alcohol-based solvent, a black dye soluble in the organic solvent, a second dye which is a yellow dye such as C.I. Acid Yellow 42, which is soluble in the organic solvent and has a polarity index of 5.0 or higher represented by a specific formula, and a resin soluble in the organic solvent (see, for example, Patent Document 3).

[0005] However, the azo iron dyes of specific structures described in Patent Documents 1 and 2 are oil-soluble black colorants, and still have issues such as unstable storage stability in oil-based solutions and insufficient fastness, particularly in lightfastness. Furthermore, there is no disclosure regarding their application to aqueous solutions or their potential for use. Similarly, the black ink composition described in Patent Document 3 is suitable for oil-based writing instrument inks, but still has issues such as unstable storage stability and insufficient lightfastness, and there is no disclosure regarding its application to aqueous solutions.

[0006] Japanese Patent Publication No. 2017-222751 (Claims, Examples, etc.), International Publication No. 2022 / 163736 (Claims, Examples, etc.), Japanese Patent Publication No. 2022-172778 (Claims, Examples, etc.)

[0007] This disclosure aims to address the problems of the prior art described above, and to provide a writing instrument ink composition that does not contain harmful heavy metals (as defined in the European standard: Toy Safety EN71-3:2019 and the International Toy Safety Standard (ISO 8124-3)), while complying with environmental impact and heavy metal regulations in various countries, and exhibiting excellent fastness, particularly lightfastness, as well as storage stability and blackness with a broad absorption spectrum.

[0008] In light of the above-mentioned conventional problems, and as a result of diligent research, we have found that, at the very least, an ink composition for writing instruments for the above-mentioned purpose can be obtained by including a specific black dye, and have completed this disclosure.

[0009] In other words, the writing instrument ink composition of this disclosure is characterized by containing at least an azo iron dye represented by the following formula (α) or the following formula (β). [In the above formula (α), R 1 These are identical or different, hydrogen atoms, and alkyl groups having 1 to 12 carbon atoms, R 2 , R 3 These are identical or different alkyl groups having 3 to 10 carbon atoms, and A +represents a monovalent ammonium ion having an alkyl group with 3 to 18 carbon atoms or an ammonium ion of a guanidine derivative.〕 〔In the above formula (β), R 1 and R 2 are each independently an alkyl group with 3 to 10 carbon atoms, linear or branched, R 3 is an electron-withdrawing group, R 4 is an alkyl group with 1 to 5 carbon atoms, linear or branched, or an alkoxy group with 1 to 5 carbon atoms, linear or branched, R 5 is a nitro group, a sulfonamide group, or a halogen atom, R 6 is a hydrogen atom, an alkyl group with 1 to 8 carbon atoms, linear or branched, a nitro group, or a halogen atom, R 7 is a hydrogen atom or an alkyl group with 3 to 12 carbon atoms, linear or branched, and A + represents a monovalent cation.〕 It is preferable to dissolve the azo iron dye represented by the above formula (α) or formula (β) in a solvent having a water solubility of 1 mass% or more. The writing instrument of the present disclosure is characterized by mounting the ink composition for writing instruments having the above configuration.

[0010] According to the present disclosure, there are provided an ink composition for writing instruments that has blackness and is excellent in drying property, water resistance, light resistance, and storage stability, and a writing instrument equipped with this ink composition for writing instruments. The objects and effects of the present disclosure are recognized and obtained by using the components and combinations particularly pointed out in the claims. Both the above general description and the following detailed description are exemplary and explanatory, and do not limit the present disclosure described in the claims.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. However, note that the technical scope of the present disclosure is not limited to each of the embodiments described in detail below, and extends to the invention described in the claims and its equivalents. The ink composition for writing instruments of the present disclosure is characterized by containing at least an azo iron dye represented by the following formula (α) or the following formula (β).

[0012] 〔In the above formula (α), R 1These are identical or different, hydrogen atoms, and alkyl groups having 1 to 12 carbon atoms, R 2 , R 3 These are identical or different alkyl groups having 3 to 10 carbon atoms, and A + This indicates a residue obtained from a monovalent ammonium ion or a guanidine derivative ammonium ion having an alkyl group with 3 to 18 carbon atoms. [In the above formula (β), R 1 and R 2 These are linear or branched alkyl groups having 3 to 10 carbon atoms, and R 3 R is an electron-withdrawing group, 4 R is a linear or branched alkyl group having 1 to 5 carbon atoms, or a linear or branched alkoxy group having 1 to 5 carbon atoms. 5 R is a nitro group, a sulfoamide group, or a halogen atom. 6 R is a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, a nitro group, or a halogen atom. 7 A is a hydrogen atom or a linear or branched alkyl group having 3 to 12 carbon atoms. + This indicates a monovalent cation.

[0013] The azo iron dyes used in this disclosure include at least one selected from azo iron dyes that are black dyes represented by the above formula (α) or (β), among dyes in which an azo dye having a complex-forming group such as a hydroxyl group (-OH) or a carboxyl group (-COOH) at the ortho position of each aromatic ring linked by an azo group (-N=N-) forms a complex salt with iron (Fe: metal).

[0014] <Azo iron dye that becomes a black dye represented by formula (α)> The azo iron dye represented by formula (α) that can be used is a complex structure in which a monoazo dye and trivalent iron form a 2:1 type complex structure, which forms an anion and is bonded to an ammonium ion. The azo iron dye represented by formula (α) is preferably the following formula (α-1) [In formula (α-1), R 2 , R 3 These are identical or different alkyl groups having 3 to 10 carbon atoms, and A + The formula is (α-2) (In formula (α-2), R 4 , R 6 These are identical or different, and represent a hydrogen atom and an alkyl group having 1 to 8 carbon atoms, R 5 represents an alkyl group having 1 to 18 carbon atoms. ) represents an ammonium ion or the following formula (α-3) (In formula (α-3), R 7 , R 8 It is an ammonium ion of a guanidine derivative represented by ), which is identical or different and represents a hydrogen atom and an alkyl group having 1 to 8 carbon atoms. It is preferable that it is an azo iron dye represented by ].

[0015] A preferred embodiment of the azo iron dye of formula (α) in this disclosure is the azo iron dye shown in formula (α-1) below. (In formula (α-1), R 2 , R 3 These are identical or different alkyl groups having 3 to 10 carbon atoms, and A + (This is a residue obtained from a monovalent ammonium ion or ammonium ion of a guanidine derivative having an alkyl group having 3 to 18 carbon atoms.) The nitro group of the substituent of the azo iron dye shown in formula (α) above has a color-deepening effect, and when substituted at the p-position of the azo group shown in formula (α-1), the color-deepening effect is maximized, resulting in a jet-black color. Furthermore, it is preferable that the counterion of the azo iron dye shown in formula (α-1) above is an ammonium ion represented by formula (α-2) or an ammonium ion of a guanidine derivative represented by formula (α-3). A mixture of ammonium ions represented by formula (α-2) or ammonium ions of a guanidine derivative represented by formula (α-3) may also be used.

[0016] The substituent R of the azo iron dye shown in formula (α) above 1The alkyl group is a linear or branched alkyl group having 1 to 12 carbon atoms, and more specifically, examples include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-pentyl group, i-pentyl group, neo-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-decyl group, lauryl group, etc. Furthermore, i-butyl group, sec-butyl group, t-butyl group, i-pentyl group, and 2-ethylhexyl group are preferred. In addition, substituent R of the azo iron dye shown in formula (α) or formula (α-1) above. 2 , R 3 The alkyl group is a linear or branched alkyl group having 3 to 10 carbon atoms, more preferably a linear or branched alkyl group having 3 to 8 carbon atoms, and more specifically, examples include n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-pentyl group, i-pentyl group, neo-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, and 2-ethylhexyl group. Furthermore, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, i-pentyl group, n-hexyl, n-octyl group, and 2-ethylhexyl group are preferred.

[0017] In the above formula (α-2), R 4 , R 6 The alkyl groups are the same or different, linear or branched alkyl groups having 1 to 8 carbon atoms, and specifically include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-pentyl group, i-pentyl group, neo-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, etc. Preferably, it is a methyl group. R in formula (α-2) 5The alkyl group is a linear or branched alkyl group having 1 to 18 carbon atoms. Specifically, examples include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-pentyl group, i-pentyl group, neo-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-decyl group, todecyl group, lauryl group, stearyl group, and the like. Preferably, it is a linear or branched alkyl group having 7 to 16 carbon atoms, and particularly preferably, it is a branched alkyl group having 8 to 15 carbon atoms.

[0018] In the above formula (α-3), R 7 , R 8 The alkyl groups are identical or different, linear or branched alkyl groups having 1 to 8 carbon atoms. Specifically, examples include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-pentyl group, i-pentyl group, neo-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, and the like. Preferably, it is a methyl group.

[0019] The black azo iron dye represented by (α) above has an amino group in its molecule, which is formed by bonding a nitro group to two alkyl groups with a specific range of carbon atoms. This causes the absorption wavelength in the visible light range to deepen, even in the azo iron complex, allowing it to exhibit a sufficiently black color for practical use. This avoids the use of certain transition metals that are avoided due to environmental concerns, such as chromium and cobalt, and also avoids the risks associated with hexavalent chromium. Furthermore, in colorants that use subtractive color mixing with the three primary colors to create a black color, the color changes significantly upon fading because each colorant has different fastness, solubility, and hue. In contrast, the black azo iron dye represented by (α) above is a single colorant that exhibits a deep black color with minimal discoloration after fading.

[0020] The method for producing the black azo iron dye represented by (α) above is known and includes at least the following steps: Step 1: obtaining a monoazo dye by a diazotization coupling reaction; Step 2: ironizing the monoazo dye to obtain an azo iron dye; Step 3: adjusting the counterions of the obtained azo iron dye; Step 4: filtering and washing the obtained azo iron dye with water; and Step 5: drying the filtered azo iron dye. By doing so, a high-purity black azo iron dye represented by (α) above can be obtained using the method described above, or a commercially available product can be used if available.

[0021] Examples of black azo iron dyes that can be specifically used, represented by (α) above, include compounds X1 to X17 and Y1 to Y9 shown in Tables 1 and 2 below, in the chemical formula shown by formula (α-4) below.

[0022]

[0023]

[0024] <Azo iron dye that becomes a black dye represented by formula (β)> Next, the black azo iron dye represented by the following formula (β) is, In the above formula (β), R 1 and R 2 These are linear or branched alkyl groups having 3 to 10 carbon atoms, and R 3 R is an electron-withdrawing group, 4 R is a linear or branched alkyl group having 1 to 5 carbon atoms, or a linear or branched alkoxy group having 1 to 5 carbon atoms. 5 R is a nitro group, a sulfoamide group, or a halogen atom. 6 R is a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, a nitro group, or a halogen atom. 7 A is a hydrogen atom or a linear or branched alkyl group having 3 to 12 carbon atoms. + This includes a disazo-monoazo iron complex represented by a monovalent cation.

[0025] The azo iron dye represented by the above formula (β) used is R 3The azo group is bonded at the para position to the azo group on the same aromatic ring, and the electron-withdrawing group may be selected from a cyano group, a nitro group, an acetyl group, a sulfoamide group, and a halogen atom. This azo iron dye is, for example, the following chemical formula (β-1) (In chemical formula (β-1), R 5 ~R 7 and A + This is identical to chemical formula (β). Examples include those containing monoazo-monoazo iron complexes represented by the following chemical formula (β-2). Azo iron dyes that can be used are those with the following chemical formula (β-2) (In chemical formula (β-2), R 1 ~R 4 and A + It may also contain a disazo-disazo iron complex represented by the chemical formula (β).

[0026] This azo iron dye, for example, has a monovalent cation that is an alkali metal ion, an ammonium ion, and the following chemical formula (β-3) (In chemical formula (β-3), R 8 R is a linear or branched alkyl group having 1 to 18 carbon atoms. 9 and R 10 Examples include at least one selected from monovalent alkyl group-containing ammonium ions, where each is independently a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms.

[0027] The azo iron dyes that can be used may have peak area ratios of 20-70:5-80:0-50, respectively, of the chromatograms obtained by measuring the disazo-monoazo iron complex, the monoazo-monoazo iron complex, and the disazo-disazo iron complex at a wavelength of 254 nm in high-performance liquid chromatography.

[0028] The method for producing the azo iron dye used is as follows: (In chemical formula (β-4), R 1 and R 2 These are linear or branched alkyl groups having 3 to 10 carbon atoms, and R 3 R is an electron-withdrawing group, 4The disazo dye represented by the following chemical formula (β-5) is a linear or branched alkyl group having 1 to 5 carbon atoms or a linear or branched alkoxy group having 1 to 5 carbon atoms.

[0029] (In chemical formula (β-5), R 5 R is a nitro group, a sulfoamide group, or a halogen atom. 6 R is a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, a nitro group, or a halogen atom. 7 The present invention provides a disazo-monoazo iron complex represented by the above chemical formula (β), comprising an iron complexization step of heating a monoazo dye represented by (where is a hydrogen atom or a linear or branched alkyl group having 3 to 12 carbon atoms) and an ironizing agent in a solvent to obtain an azo iron complex anion, and an ion exchange step of reacting the azo iron complex anion with an alkali metal solution and / or an ammonium agent to introduce a cation to be combined with the azo iron complex anion.

[0030] The disazo-monoazo iron complex contained in the azo iron dye used has a structure in which a monovalent cation is bonded to an azo iron complex anion containing trivalent iron and an azo ligand formed by combining the disazo dye and the monoazo dye in a 1:2 molar ratio, as can be seen from the above formula (β). In the above formula (β), R 1 and R 2These are linear or branched alkyl groups having 3 to 10 carbon atoms. Specifically, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, 2-methylpentyl group, 3-methylpentyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, n-heptyl group, 2-methylhexyl group, 3-methylhexyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2,4-dimethylpentyl group, 3,3-dimethylpentyl group, 3-ethylpentyl group, 2,2,3-trimethylbutyl group, n-octyl group, 2-methylheptyl group, 3-methylheptyl Examples of groups include 4-methylheptyl group, 2,2-dimethylhexyl group, 2,3-dimethylhexyl group, 2,4-dimethylhexyl group, 2,5-dimethylhexyl group, 3,3-dimethylhexyl group, 3,4-dimethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group, 2,2,3-trimethylpentyl group, 2,2,4-trimethylpentyl group, 2,3,3-trimethylpentyl group, 2,3,4-trimethylpentyl group, 2-methyl-3-ethylpentyl group, 3-methyl-3-ethylpentyl group, and 2,2,3,3-tetramethylbutyl group, n-nonyl group, n-decyl group, and lauryl group. Among these, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, and 2-ethylhexyl group are preferred. In the above formula (β), R 3 R is an electron-withdrawing group, specifically including cyano groups, nitro groups, acetyl groups, sulfoamide groups, and halogen atoms. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine. 3 When these are electron-withdrawing groups, the color-deepening effect of the azo iron dye is enhanced, resulting in a sufficiently deep black color for practical use. 3 It is preferable in terms of deepening the color if the compound is bonded to the azo group on the same aromatic ring at the para position.

[0031] Such disazo-monoazo iron complexes are specifically represented by the following chemical formula (β-6) (In chemical formula (β-6), R 1 ~R 7 and A +This is identical to the chemical formula (β). It is represented as ). In the chemical formula (β-6), R 4 This group is a linear or branched alkyl group having 1 to 5 carbon atoms, or a linear or branched alkoxy group having 1 to 5 carbon atoms. Specifically, examples of this alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and neopentyl groups, and examples of this alkoxy group include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentyloxy, isopentyloxy, and neopentyloxy groups.

[0032] Such disazo-monoazo iron complexes are specifically represented by the following chemical formula (β-7) (In chemical formula (β-7), R 1 ~R 7 and A + This is identical to the chemical formula (β). It is represented as ). In the chemical formula (β-7), R 5 R is an electron-withdrawing substituent such as a nitro group, a sulfoamide group, or a halogen atom. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine. 5 It is preferable that the azo group is bonded to the 4th or 5th position relative to the azo group on the aromatic ring to which it is bonded, as this further improves the blackness of the disazo-monoazo iron complex and allows for a sufficiently deep black color to be obtained for practical use.

[0033] In the chemical formula (β), R 6is a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, a nitro group, or a halogen atom. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,3-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an n-octyl group, a 2-methylheptyl group, a 3-methylheptyl group, a 4-methylheptyl group, a 2,2-dimethylhexyl group, a 2,3-dimethylhexyl group, a 2,4-dimethylhexyl group, a 2,5-dimethylhexyl group, a 3,3-dimethylhexyl group, a 3,4-dimethylhexyl group, a 2-ethylhexyl group, a 3-ethylhexyl group, a 2,2,3-trimethylpentyl group, a 2,2,4-trimethylpentyl group, a 2,3,3-trimethylpentyl group, a 2,3,4-trimethylpentyl group, a 2-methyl-3-ethylpentyl group, a 3-methyl-3-ethylpentyl group, and a 2,2,3,3-tetramethylbutyl group. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine.

[0034] Such a disazo-monoazo iron complex is specifically represented by the following chemical formula (β-8a) (In the chemical formula (β-8a), R 1 to R 7 and A + are the same as those in the chemical formula (β).) and the following chemical formula (β-8b) (In the chemical formula (β-8b), R 1 to R 7 and A + are the same as those in the chemical formula (β).)

[0035] In the chemical formulas (β-8a) and (β-8b), R 7is a hydrogen atom or a linear or branched alkyl group having 3 to 12 carbon atoms. Examples of such alkyl groups include n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, 2-methylpentyl group, 3-methylpentyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, n-heptyl group, 2-methylhexyl group, 3-methylhexyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2,4-dimethylpentyl group, 3,3-dimethylpentyl group, 3-ethylpentyl group, 2,2,3-trimethylbutyl group, n-octyl group, tert-octyl group, 2-methylheptyl group, 3-methylheptyl group, 4-methylheptyl group, 2,2-dimethylhexyl group, 2,3-dimethylhexyl group, 2,4-dimethylhexyl group, 2,5-dimethylhexyl group, 3,3-dimethylhexyl group, 3,4-dimethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group, 2,2,3-trimethylpentyl group, 2,2,4-trimethylpentyl group, 2,3,3-trimethylpentyl group, 2,3,4-trimethylpentyl group, 2-methyl-3-ethylpentyl group, 3-methyl-3-ethylpentyl group, and 2,2,3,3-tetramethylbutyl group, n-nonyl group, n-decyl group, lauryl group, and dodecyl group. Among them, tert-butyl group, isopentyl group, hexyl group, n-octyl group, tert-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, and dodecyl group are preferred.

[0036] Such a diazo-monoazo iron complex is specifically represented by the following chemical formula (β-9a) (In the chemical formula (β-9a), R 1 to R 7 and A + are the same as those in the chemical formula (β).), the following chemical formula (β-9b) (In the chemical formula (β-9b), R 1 to R 7 and A + are the same as those in the chemical formula (β).), the following chemical formula (β-9c) (In the chemical formula (β-9c), R 1 to R 7and A + This is identical to the chemical formula (β), and the following chemical formula (β-9d) (In chemical formula (β-9d), R 1 ~R 7 and A + This is identical to the chemical formula (β).

[0037] In the chemical formula (β) above, A + It is a monovalent cation. Examples of this monovalent cation include hydrogen ions, alkali metal ions, and ammonium ions (NH4). + Examples include ammonium ions containing monovalent alkyl groups. The disazo-monoazo iron complex may have only one or more of these monovalent cations. Among these, ammonium ions and monovalent alkyl group-containing ammonium ions are preferred. As alkali metal ions, lithium ions (Li + ), sodium ions (Na + ), and potassium ions (K + Examples include the following. The alkali metal ions may originate from pH adjusters used in the synthesis process of the disazo-monoazo iron complex. Furthermore, the monovalent cation may be bonded to the iron complex anion by only one type, or by multiple types.

[0038] A monovalent alkyl group-containing ammonium ion is represented by the following chemical formula (β-3). In the above chemical formula (β-3), R 8 R is a linear or branched alkyl group having 1 to 18 carbon atoms. 9 and R 10 R is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, independently of each other. 7The alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, 2-methylpentyl group, 3-methylpentyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, n-heptyl group, 2-methylhexyl group, 3-methylhexyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2,4-dimethylpentyl group, 3,3-dimethylpentyl group, 3-ethylpentyl group, 2,2,3-trimethylbutyl group, n-octyl group, 2-methylheptyl group, and 3-methylheptyl Examples of methylhexyl groups include 4-methylheptyl group, 2,2-dimethylhexyl group, 2,3-dimethylhexyl group, 2,4-dimethylhexyl group, 2,5-dimethylhexyl group, 3,3-dimethylhexyl group, 3,4-dimethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group, 2,2,3-trimethylpentyl group, 2,2,4-trimethylpentyl group, 2,3,3-trimethylpentyl group, 2,3,4-trimethylpentyl group, 2-methyl-3-ethylpentyl group, 3-methyl-3-ethylpentyl group, and 2,2,3,3-tetramethylbutyl group, n-nonyl group, n-decyl group, undecyl group, lauryl group, and stearyl group. In particular, it is preferable that the alkyl group has 7 to 18 carbon atoms and is linear or branched, more preferably that it has 8 to 15 carbon atoms and is branched, and even more preferably that it has 11 to 14 carbon atoms and is branched.

[0039] In the above chemical formula (β-3), R 9 and R 10 Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, n-heptyl, and n-octyl groups. Among these, the methyl group is preferred. The disazo-monoazo iron complex, which is essential to the azo iron dye represented by (β) above in this disclosure, is an amino group to which a dialkyl group having a specific range of carbon atoms is bonded (the -NR in chemical formula (β)). 1 R 2 ) and electron-withdrawing groups (same -R3 A disazo ligand having a disazo ligand and an electron-withdrawing group (same -R) 5 and / or -R 6 Due to its asymmetrical structure containing a monoazo ligand, the azo iron dye deepens in color, absorbing wavelengths in the visible light range and exhibiting a deep black color sufficient for practical use. Moreover, the aromatic ring of the disazo ligand is composed solely of arylene groups and does not contain a naphthalene ring, which is bulky and causes high molecular weight. Therefore, this azo iron dye has a lower molecular weight compared to azo iron dyes containing a naphthalene ring-containing disazo ligand, and thus exhibits high color development even in small amounts.

[0040] Furthermore, this disazo-monoazo iron complex has alkali metal ions, ammonium ions, and / or monovalent alkyl group-containing ammonium ions having an alkyl group with a specific range of carbon atoms as cations, thereby improving the solubility of the black azo iron complex anion. As a result, the azo iron dye represented by (β) above exhibits high solubility that is practical as an ink composition in alcohol-based organic solvents such as ethanol and ethylene glycol, and ketone-based organic solvents such as methyl ethyl ketone, and also has high solubility stability, so it does not precipitate or precipitate in organic solvents. Moreover, the azo iron dye does not contain chromium or cobalt, which are heavy metals harmful to the environment and human body, so it can contribute to environmental protection and ensure safety for the human body. In addition to the disazo-monoazo iron complex represented by the chemical formula (β) above, it is preferable to further include a monoazo-monoazo iron complex having only the monoazo ligand, which is a ligand of this disazo-monoazo iron complex, and / or a disazo-disazo iron complex having only the disazo ligand.

[0041] This monoazo-monoazo iron complex is the same as the chemical formula (β-1) (where R is located in the chemical formula (β-1)). 5 ~R 7 and A + The chemical formula (β) is the same as the chemical formula (β). The disazo-disazo iron complex is represented by the above chemical formula (β-2) (in the chemical formula (β-2), R 1 ~R 4 and A +The chemical formula (β) is the same as (β). When the azo iron dye represented by (β) that can be used includes disazo-monoazo iron complex (DM), monoazo-monoazo iron complex (MM), and disazo-disazo iron complex (DD), their molar ratios can be expressed as the peak area ratio in the chromatogram obtained when measured by high-performance liquid chromatography at a specific wavelength, for example, 254 nm. Specifically, it is preferable that DM:MM:DD = 20-70:5-80:0-50, more preferably 20-65:5-80:0-50, even more preferably 20-60:20-80:0-30, and still more preferably 20-55:20-80:0-15. The lower limit for the DD is 1 instead of 0. Note that the above values ​​are obtained by calculating the peak area ratio to one decimal place and rounding it. For example, the notation 0, which is the lower limit for the DD field, includes values ​​greater than 0.0, namely 0.1 to 0.4.

[0042] The azo iron dye represented by (β) above contains, in addition to the asymmetric azo iron complex, the disazo-monoazo iron complex, as well as symmetric azo iron dyes such as a monoazo-monoazo iron complex having only a monoazo ligand and / or a disazo-disazo iron complex having only a disazo ligand. By setting the ratio of each azo iron complex in the azo iron complex within an appropriate range, the blackness, solubility, and solubility stability of the azo iron dye can be further improved. Furthermore, the electrical conductivity K of the azo iron dye represented by (β) above is preferably 300 to 2200 μS / cm, and more preferably 600 to 2000 μS / cm. This electrical conductivity K is measured by inserting the electrodes of an electrical conductivity meter into a 6% by mass methyl ethyl ketone solution of the azo iron dye and immersing them. Furthermore, the alkali metal ion content of the azo iron dye is preferably 1000 ppm or less, and more preferably 500 ppm or less. Furthermore, additives such as leveling agents and anti-repellent agents contained in writing instrument ink compositions may contain silicone compounds or silicone-based surfactants. If the alkali metal ion content of the azo iron dye is within the above range, the formation of complexes between these silicone compounds and silicone-based surfactants and alkali metal ions can be suppressed, thereby preventing clogging in the ink reservoir and pen tip.

[0043] The production of azo iron dyes containing azo iron complexes represented by the above chemical formulas (β) to (β-2) is known, and can be carried out, for example, by employing a production method having the following first to fifth steps: First step: A step to obtain a disazo dye using a diazo coupling reaction. Second step: A step to obtain a monoazo dye using a diazo coupling reaction. Third step: A step to obtain an azo iron dye by iron-complexing a mixture of disazo dye and monoazo dye. Fourth step: A step to change and prepare the cation of the azo iron dye. Fifth step: A step to filter, wash, dry, and pulverize the azo iron dye. According to this production method, azo iron dyes containing azo iron complexes represented by the above chemical formulas (β) to (β-2), etc., can be of high purity. The black azo iron dye represented by (β), etc., can be the one obtained by the above production method, or if a commercially available product is available, that can be used.

[0044] Examples of black azo iron dyes represented by the above formula (α) or (β) that can be specifically used are listed below. An example of a black azo iron dye represented by the above formula (α) is the azo iron dye shown in the following formula (α-5). The production of this azo iron dye shown in formula (α-5) is known and is briefly described below. The amount of each component used, the reaction time, the reaction temperature, etc. are predetermined amounts, predetermined time, predetermined temperature, etc.

[0045] The azo iron dye represented by formula (α-5) was prepared by dissolving 5-nitro-2-aminophenol and 35 wt% concentrated hydrochloric acid in isopropanol as starting materials, and gradually adding a 36 wt% aqueous sodium nitrite solution while cooling in an ice bath to diazotize and obtain a diazonium salt. Meanwhile, a 20 wt% aqueous sodium hydroxide solution was added to water, and N,N-di-n-butyl-3-aminophenol was added and dispersed. The diazonium salt was then added dropwise to this dispersion and reacted. After that, the pH was adjusted to 2.6, the precipitated monoazo compound was filtered off and washed with water to obtain a predetermined amount of wet cake. To the obtained wet cake of monoazo compound, a 20 wt% aqueous sodium hydroxide solution, water, and n-butanol were added and stirred at a predetermined temperature for a predetermined time, and then a 40 wt% aqueous ferric sulfate solution was gradually added and the reaction was carried out at a predetermined temperature for a predetermined time. After the reaction, the mixture was cooled to room temperature and adjusted to pH 2.5. The precipitated product was filtered and washed with water to obtain a wet cake. Water and methanol were added to the wet cake of the iron complex compound and heated to a predetermined temperature. An aqueous solution prepared in advance with water, 35 wt% concentrated hydrochloric acid, and 1,3-di-O-tolylguanidine was gradually added to this solution. After stirring at a predetermined temperature for an initial time, the mixture was filtered, washed with water, and dried to obtain the azo iron dye represented by the above formula (α-5).

[0046] Examples of black azo iron dyes represented by the above formula (β) include the disazo dye D-1 shown in the following formula (β-10a) and the monoazo dye M-1 shown in the following formula (β-10b), and the azo iron dyes shown in the following formulas (β-11a), (β-11b), and (β-11c).

[0047] The production of azo iron dyes represented by formulas (β-11a), (β-11b), and (β-11c) is known and is briefly described below. The production of azo iron dyes represented by each of these formulas is as follows: Disazo dye D-1 of formula (β-10a) and monoazo dye M-1 of formula (β-10b) are added to an N,N-dimethylformamide solution and stirred at a predetermined temperature for a predetermined time (disazo dye:monoazo dye = 2:8 mol). A 41% ferric sulfate aqueous solution is added dropwise, and after the addition is complete, the temperature is raised to a predetermined temperature and stirred for a predetermined time. After the reaction is complete, the mixture is allowed to cool to room temperature, a 20% sodium hydroxide aqueous solution is added to adjust the pH to 10.0, and a 5% tert-alkyl (C12-C14) primary amine aqueous solution is gradually added to the reaction solution and heated and stirred at a predetermined temperature for a predetermined time. Subsequently, the precipitate was filtered, washed with water, and dried to obtain an azo iron complex dye containing the disazo-monoazo iron complex represented by the above chemical formula (β-11a) (DM form), the monoazo-monoazo iron complex represented by the above chemical formula (β-11b) (MM form), and the disazo-disazo iron complex represented by the above chemical formula (β-11c) (DD form).

[0048] <Ink Composition for Writing Instruments> The ink composition for writing instruments of this disclosure is characterized by containing at least one black dye selected from azo iron dyes that are black dyes represented by formula (α) or formula (β) above, and can be used as an ink composition for writing instruments such as ballpoint pens and marking pens. Preferably, from the viewpoint of color development, drying speed, water resistance, and not containing regulated heavy metals, it is preferable to dissolve the azo iron dye represented by formula (α) or formula (β) in a solvent with a water solubility of 1% by mass or more. "Water solubility" as defined in this disclosure means solubility in water at 25°C (water solubility). Examples of solvents with a water solubility of 1% by mass or more include methanol, ethanol, propylene glycol monomethyl ether, isopropanol, 1-propanol, butanol, 3-methoxy-3-methyl-1-butanol, tert-butanol, 2-ethylhexanol, benzyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, glycerin, diglycerin, methyl carbitol, cyclohexanol, ethyl carbitol, butyl carbitol, and methyl triglycol. More preferably, ethanol (water solubility 100%), isopropanol (water solubility 100%), 1-propanol (water solubility 10%), 3-methoxy-3-methyl-1-butanol (water solubility 10%), benzyl alcohol (water solubility 3.5%), and ethyl acetate (water solubility 8.7%) are used. As a method for preparing a solvent with a water solubility of 1% by mass or more, formula (α) or formula (β) can be easily prepared, for example, by stirring at room temperature for 2 hours.

[0049] This disclosure provides a writing instrument ink composition that has a predetermined degree of blackness in both oil-based and aqueous inks, while also exhibiting excellent lightfastness and storage stability, by using a solution of an azo iron dye represented by formula (α) or formula (β) dissolved in a solvent having a water solubility of 1% by mass or more. The content of the azo iron dye, which is the black dye represented by formula (α) or formula (β) in this disclosure, is preferably 0.01 to 40.0% by mass, more preferably 0.01 to 30.0% by mass, even more preferably 0.01 to 25.0% by mass, particularly preferably 0.1 to 20.0% by mass, and most preferably 1.0 to 15.0% by mass, based on the total amount of the aqueous or oil-based ink composition. If the content of this azo iron dye is less than 0.01% by mass, the coloring power and color development will be insufficient, while if it exceeds 40.0% by mass, streaking will easily occur, which is undesirable.

[0050] Furthermore, this disclosure suggests that further improvements in blackness can be expected by using a material that absorbs at a specific wavelength in combination with the black dye represented by formula (α) or formula (β). Specifically, by using a solution prepared by dissolving the azo iron dye represented by formula (α) or formula (β) and a material that absorbs at a specific wavelength in a solvent with a water solubility of 1% by mass or more, it is possible to create a writing instrument ink composition that achieves an even higher level of balance between lightfastness and blackness in both oil-based and water-based inks, and has excellent storage stability.

[0051] Other materials besides the azo iron dye represented by formula (α) or formula (β), such as complementary dyes, may be used in combination, and further improvement in blackness can be expected. Examples of materials that may be used in combination include: Oil-soluble dyes such as commercially available monoazo, disazo, metal complex type monoazo, anthraquinone, phthalocyanine, and triarylmethane. Salt-forming type oil-soluble dyes, in which functional groups such as acid and basic dyes are replaced with hydrophobic groups, can also be used. Examples of yellow dyes include C.I. Solvent Yellow 14, 16, 29, 30, 33, 56, 62, 93, 98, 114, 116, 151, 157, 162, and Basic Yellow 40; examples of orange dyes include C.I. Solvent Orange 22, 45, and 67; and examples of red dyes include C.I. Examples of color combinations include Solvent Red 3, 18, 49, 146 and Basic Red 1, 1:1; for blues, C.I. Solvent Blue 5, 35, 36, 44, 63, 70, 83, 105, 111 and Basic Blue 1; for blacks, C.I. Solvent Black 3, 7, 29; and for purples, C.I. Basic Violet 1, 11:1, etc. Specific examples of commercially available oil-soluble dyes include the blue dye SBN Blue 701 (manufactured by Hodogaya Chemical Co., Ltd.), the blue dye Oil Blue 650 (manufactured by Orient Chemical Industry Co., Ltd.), the blue dye Savinyl Blue GLS (manufactured by Clariant Co., Ltd.), the red dye SOC-1-0100 (manufactured by Orient Chemical Industry Co., Ltd.), Oil Black 860, Oil Pink 314, Oil Yellow 129, Oil Yellow 3G, Oil Yellow CGHNnew, Oil Yellow 1108 (manufactured by Orient Chemical Industry Co., Ltd.). The (total) content of these materials (complementary dyes, etc.) is preferably 0.01 to 40.0% by mass, and more preferably 0.2 to 25.0% by mass, relative to the total amount of the aqueous or oil-based ink composition, taking into consideration the range that can comply with heavy metal regulations, and from the viewpoint of further improving blackness and storage stability.

[0052] <Aqueous Ink Composition for Writing Instruments> In the aqueous ink composition for writing instruments of this disclosure, in addition to the azo iron dye of formula (α) or formula (β) above, the remainder may be water as a solvent (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.), and depending on the application for each writing instrument (for ballpoint pens, marking pens, etc.), water-soluble organic solvents, thickeners, lubricants, rust inhibitors, humectants, preservatives or antibacterial agents may be appropriately included to the extent that the effects of this disclosure are not impaired.

[0053] 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, as well as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether, which can be used alone or in combination.

[0054] The thickening agents that can be used are preferably at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides. Specifically, examples include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, gelan gum, succinoglycan, dieutan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid and its salts, propylene glycol alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, carboxyvinyl polymer, polyethylene hydroxide, copolymer of vinyl acetate and polyvinylpyrrolidone, crosslinked acrylic acid polymer and its salts, non-crosslinked acrylic acid polymer and its salts, styrene acrylic acid copolymer and its salts, and the like.

[0055] Examples of lubricants include nonionic compounds such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, higher polyoxyalkylene fatty acid esters, and alkyl phosphate esters, which are also used as surface treatment agents for pigments; anionic compounds such as alkyl sulfonates and alkyl allyl sulfonates of higher fatty acid amides; derivatives of polyalkylene glycols; fluorinated surfactants; and polyether-modified silicones. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitride, and saponins, while examples of preservatives or antibacterial agents include phenol, sodium omazine, sodium benzoate, and benzimidazole compounds.

[0056] In this disclosure, preferably, in order to further improve the non-drying properties of the pen tip, the storage stability of the ink, and to obtain stability over time at high temperatures, sugar alcohols and / or glycine betaine [also known as trimethylglycine, (CH3)2N] are used as humectants. + (CH3)CH2COO -It is desirable that the product contains glycine betaine and disaccharides or more, with pentasaccharides or more making up 50% by mass or more of the total amount of disaccharides or more of the sugar alcohols. Commercially available products include SE20 (manufactured by Bussan Food Science Co., Ltd., containing approximately 5-20% by mass of sugar alcohols with five or more saccharides) and SE600 (manufactured by Bussan Food Science Co., Ltd., containing approximately 1-5% by mass of sugar alcohols with five or more saccharides). Furthermore, sugar alcohols in which 50% or more by mass consist of sugar alcohols with an average degree of polymerization of 5 or more relative to the total amount of sugar alcohols with two or more saccharides include, for example, H-PDX [containing approximately 75% by mass of sugar alcohols with five or more saccharides (pentasaccharide: 6.4% by mass, hexasaccharide: 10% by mass, heptasaccharide: 58.5% by mass), manufactured by Matsutani Chemical Industry Co., Ltd.] and SE100 (manufactured by Bussan Food Science Co., Ltd., containing approximately 64-82% by mass of sugar alcohols with five or more saccharides).

[0057] The content of these sugar alcohols and / or humectants such as glycine betaine is preferably 0.5 to 10% by mass, and more preferably 1 to 5% by mass, relative to the total amount of the aqueous ink composition for writing instruments, from the viewpoint of ink discharge performance and ink storage stability. If the content is less than 0.5% by mass, the non-drying properties of the pen tip cannot be further improved, on the other hand, if it exceeds 10% by mass, the ink viscosity will increase, impairing the quality of the lines, such as causing smudging during writing.

[0058] This aqueous ink composition for writing instruments can be manufactured using conventionally known methods. For example, it can be obtained by mixing a predetermined amount of the above aqueous components with an azo iron dye represented by formula (α) or formula (β) or a solution obtained by dissolving the azo iron dye in a solvent with a water solubility of 1% or more, and stirring and mixing them with a stirrer such as a homomixer or disperser. Furthermore, if necessary, coarse particles in the ink composition may be removed by filtration or centrifugation. In addition, the aqueous ink composition for writing instruments may be prepared as an emulsion ink. Emulsified inks are divided into O / W type inks, which are contained in the form of an oil-in-water emulsion, and W / O type inks, which are contained in the form of an oil-in-oil emulsion. In O / W type inks, a high HLB emulsifier can be used, for example, by mixing an aqueous solution of sodium dodecyl sulfate in a range of 5 to 20% by mass. In W / O type inks, low HLB emulsifiers can be used, and this can be adjusted by using, for example, polyoxyethylene (9) nonylphenyl ether (Igepal CO-630), POE isodecyl ether (Nonion ID-209 manufactured by NOF Corporation), or phenol ethoxylate (Adekatol SP-12 manufactured by ADEKA Corporation). In the case of O / W type inks, the average particle size of the oil droplets in the oil-in-water emulsion is preferably 20 to 800 nm in terms of dispersion stability of the emulsified droplets and overall ink uniformity. The oil phase is preferably viscous at 25°C and a shear rate of 38 / second to 500,000 mPa·s in terms of uniformity of the emulsified ink. In addition, in the aqueous ink composition for writing instruments of this disclosure, other pigments such as microcapsule pigments that change color with heat or light, colored resin particles in which dyes are applied to resins, and white resin particles can be used in combination, to the extent that the effects of the invention are not impaired.

[0059] <Oil-based ink composition for writing instruments> In the writing instrument ink composition of the present disclosure, in the oil-based version, it is preferable to contain an azo iron dye represented by formula (α) or formula (β) of the above configuration, or a solution obtained by dissolving the azo iron dye in a solvent with a water solubility of 1% by mass or more, and to contain at least one selected from polypropylene glycol, polybutylene glycol, polyoxypropylene diglyceryl ether, and glycol ethers as the main solvent. By selecting and using these solvents as the main solvent, it is possible to prevent the azo iron dye represented by formula (α) or formula (β) from agglomerating over time.

[0060] While polypropylene glycol and polybutylene glycol of various degrees of polymerization can be used, to further enhance the effects of this disclosure, it is preferable to use polypropylene glycol with a degree of polymerization (weight average) in the range of 400 to 700, and polybutylene glycol with a degree of polymerization (weight average) in the range of 500 to 700. Furthermore, the polyoxypropylene diglyceryl ether [POP(n) diglyceryl ether] used in this disclosure is obtained by addition polymerization of polyoxypropylene to the hydroxyl groups of diglycerin. In this disclosure, the number of moles (n) of oxypropylene added to the polyoxypropylene diglyceryl ether [POP(n) diglyceryl ether] is preferably 4 to 25, and more preferably 4 to 14, to further enhance the effects of this disclosure. Among glycol ethers, those having 2 to 7 carbon atoms are particularly preferred, specifically including 1,3-butanediol, 3-methyl-1,3-butanediol, 3-methoxy-butanol, 3-methyl-3-methoxy-butanol, and hexylene glycol.

[0061] The content of these main solvents is preferably 50 to 100% by mass, and more preferably 80 to 100% by mass, relative to the total amount of solvent in the oil-based ink composition. By having a main solvent content of 50% by mass or more, the occurrence of aggregation over time can be suppressed as much as possible. In addition to the main solvents mentioned above, solvents that are compatible with the main solvents, such as glycerin, diglycerin, and propylene glycol, can be appropriately included, as long as they do not impair the effects of this disclosure.

[0062] This oil-based ink composition for writing instruments contains, in addition to the azo iron dye represented by (α) or formula (β) above, or a solution obtained by dissolving the azo iron dye in a solvent with a water solubility of 1% by mass or more, and a main solvent, it may also contain resins, dispersants, rust inhibitors, preservatives, lubricants, ink drip inhibitors, etc., that are compatible with each writing instrument (for ballpoint pens, marking pens, etc.) and as needed, without adversely affecting the oil-based ink. Examples of resins that can be used include ketone resins, styrene resins, styrene-acrylic resins, terpene phenol resins, rosin-modified maleic acid resins, rosin-phenol resins, alkylphenol resins, phenolic resins, styrene-maleic acid resins, rosin-based resins, acrylic resins, urea aldehyde-based resins, maleic acid-based resins, cyclohexanone-based resins, polyvinyl butyral, polyvinylpyrrolidone, and the like. Polyvinyl butyral can be used to adjust the viscosity of the oil-based ink composition for writing instruments. In this case, the mass-average molecular weight of polyvinyl butyral may be 10,000 or more, 20,000 or more, 30,000 or more, 40,000 or more, 50,000 or more, 60,000 or more, 70,000 or more, 80,000 or more, 90,000 or more, 100,000 or more, or 105,000 or more, and can also be 150,000 or less, 140,000 or less, 130,000 or less, 120,000 or less, or 115,000 or less. The content of the aforementioned resin is preferably 0.1 to 10% by mass, and more preferably in the range of 0.2 to 8% by mass or 0.3 to 7% by mass, based on the total mass of the oil-based ink composition for writing instruments.

[0063] In the oil-based ink composition for writing instruments disclosed herein, pigments may be used in combination, to the extent that they do not impair the effects of the invention. As a pigment dispersant, resins such as those listed above can be appropriately selected and used. Surfactants and oligomers can also be included if they are suitable for the purpose. Specific dispersants include, for example, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, polyvinyl ether, styrene-maleic acid copolymer, ketone resin, synthetic resins such as hydroxyethylcellulose and its derivatives, and styrene-acrylic acid copolymer, as well as PO / EO adducts and polyester amine oligomers. Furthermore, as rust inhibitors, preservatives, and lubricants, the various rust inhibitors, preservatives, and lubricants used in aqueous solutions as described above can be used.

[0064] As an ink drip prevention agent, fine silica particles can be used, with a specific surface area of ​​50 m². 2 It is preferable to use fine particle silica with a specific surface area of ​​50 m² / g or more, and is particularly suitable when used as an ink composition for oil-based ballpoint pens. The fine particle silica used in this disclosure has a specific surface area of ​​50 m². 2 It is 1 / g or more, preferably 80m 2 / g, more preferably 100m 2 It is 1 / g or more. The specific surface area is 50 m². 2If the amount is less than / g, the primary particle size is large and the above effects are difficult to obtain. Fine particle silica can be commercially available, for example, hydrophobic grades such as R972, R972V, R972CF, R974, R202, R805, R812, and R812S of the AEROSOL series manufactured by Nippon Aerosil Co., Ltd., or hydrophilic grades such as 50, 130, 200, 300, 380, and TT600 of the AEROSOL series manufactured by Nippon Aerosil Co., Ltd. The fine particle silica used in this disclosure is preferably one whose silica surface has been hydrophobicized. If many hydrophilic groups remain on the silica surface, the hydrophilic groups are likely to interact with other silica particles or dispersants, making it difficult to obtain an oil-based ink composition for writing instruments that is stable over time, in addition to preventing ink dripping. In this disclosure, it is desirable that the oil-based ink composition for writing instruments contains 0.01 to 5% by mass, more preferably 0.1 to 4.0% by mass, and particularly preferably 0.5 to 3.0% by mass, of fine particles of silica in order to prevent ink dripping from the pen tip and to ensure storage stability.

[0065] To manufacture this oil-based ink composition for writing instruments, conventionally known methods can be employed. For example, it can be obtained by mixing a predetermined amount of the above-mentioned oil-based components with an azo iron dye represented by formula (α) or formula (β) above, or a solution obtained by dissolving the azo iron dye in a solvent with a water solubility of 1% by mass or more, and stirring and mixing them with a stirrer such as a homomixer or disperser. Furthermore, if necessary, coarse particles in the ink composition may be removed by filtration or centrifugation. In addition, the oil-based ink composition for writing instruments may be prepared using the above-mentioned solvent, resin, dispersant, etc., in the range of low viscosity (ink viscosity (25°C) at a shear rate of 38.3 / s in the range of 1 to 30 mPa·s) or high viscosity (ink viscosity (25°C) at a shear rate of 38.3 / s in the range of 100 to 10000 mPa·s). The viscosity in each range can be measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd.). The oil-based ink composition for writing instruments may also be used as a W / O type ink, further contained in the form of a water-in-oil emulsion. Depending on the viscosity range, these writing instrument ink compositions can be appropriately selected to take the form of a felt-tip pen, ballpoint pen, etc.

[0066] In this disclosure, in the aqueous ink composition for writing instruments and the oil-based ink composition for writing instruments, it is desirable to use anionic or nonionic surfactants together with the black dye represented by formula (α) or formula (β) above, from the viewpoint of quick drying of the lines and resistance to bleeding, and the effects can be fully exhibited when included in an amount of 0.01 to 5.0% by mass, preferably 0.05 to 3.0% by mass, and particularly preferably 0.1 to 2.0% by mass, based on the total amount of the aqueous or oil-based ink composition. Furthermore, at least one of the anionic surfactants can be found among phosphate esters, polyalkylene glycol derivatives such as polyoxyethylene lauryl ether, fatty acid alkali salts, nonionic surfactants, fluorine-based surfactants such as perfluoroalkyl phosphate esters, polyether-modified silicones such as polyethylene glycol adducts of dimethylpolysiloxane, acetylene glycols and acetylene derivatives selected from their ethylene oxide adducts.Specifically, this includes Aqualon AN-10, AN-20, AN-30, AN-5065 (all polyoxyethylene styrene-propenylphenyl ether: EO addition moles 10, 20, 30, 40, 50) and Aqualon RN-10, RN-20, RN-30, RN-50 (all polyoxyethylene propenylphenyl ether (nonylphenyl type): EO addition moles 10, 20, 30, 50) from Daiichi Kogyo Seiyaku Co., Ltd., Latemul PD-420, PD-430, PD-450 (all polyoxyalkylene alkenyl ether) from Kao Corporation, Bremmer PE-90, PE-200, PE-350 (all PEG monomethacrylate: EO addition moles 2, 4.5, 8) and Bremmer AE-200, AE-400 (all PEG monoacrylate: EO addition moles) from NOF Corporation. Numbers 4, 5, 10), Bremmer PP-1000, PP-500, PP-800 (all PPG monomethacrylate: PO addition moles 4-6, 9, 13), Bremmer AP-200, AP-400, AP-550, AP-800 (all PPG monoacrylate: PO addition moles: 3.5, 6, 9, 13), NOF Corporation's Uniox PKA-5001, PKA-5002, PKA-5 Examples include 003, PKA-5004, Unisafe PKA-5014F, Adeka's Adeka Soap ER-10, ER-20, ER-30, ER-40 (all alkyl type: EO addition moles: 10, 20, 30, 40), and Adeka Soap NE-10, NE-20, NE-30 (all alkylphenol type: (nonylphenyl type) EO addition moles: 10, 20, 30).

[0067] In this disclosure, it is preferable that the above-mentioned aqueous ink compositions for writing instruments and oil-based ink compositions for writing instruments further contain an ultraviolet absorber and / or a light stabilizer in order to further enhance lightfastness and storage stability against light. Conventional ultraviolet absorbers can be used, such as benzotriazole absorbers, triazine absorbers, salicylic acid derivative absorbers, and benzophenone absorbers, and it is preferable that the above ultraviolet absorbers have polymerizable unsaturated groups.

[0068] Specific examples of benzotriazole absorbents include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chloro Examples include lobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzotriazole, 2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole, 2-{2'-hydroxy-3'-(3'',4'',5'',6''-tetrahydrophthalimidomethyl)-5'-methylphenyl}benzotriazole, and 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole.

[0069] Specific examples of triazine-based absorbents include 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-isooctyloxyphenyl)-1,3,5-triazine, 2-[4((2-hydroxy-3-dodecyloxypropyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-((2-hydroxy-3-tridecyloxypropyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, and 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine.

[0070] Specific examples of salicylic acid derivative-based absorbents include phenyl salicylate, p-octylphenyl salicylate, and 4-tert-butylphenyl salicylate. Specific examples of benzophenone-based absorbents include 4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone trihydrate, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-octadecyloxybenzophenone, and sodium Examples include lium-2,2'-dihydroxy-4,4'-dimethoxy-5-sulfobenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 5-chloro-2-hydroxybenzophenone, resorcinol monobenzoate, 2,4-dibenzoylresorcinol, 4,6-dibenzoylresorcinol, hydroxydodecylbenzophenone, and 2,2'-dihydroxy-4(3-methacrylateoxy-2-hydroxypropoxy)benzophenone.

[0071] Examples of commercially available UV absorbers include "Tinuvin 900," "Tinuvin 928," "Tinuvin 348-2," "Tinuvin 479," "Tinuvin 405," and "Tinuvin 400" (all manufactured by BASF, trade names; Tinuvin is a registered trademark), and "RUVA-93" (both manufactured by Otsuka Chemical Co., Ltd., trade names). The amount of this UV absorber can be 0.1 to 20.0% by mass, and preferably 1.0 to 10.0% by mass, relative to the total amount of the aqueous or oil-based ink composition, from the viewpoint of further lightfastness and storage stability.

[0072] Suitable light stabilizers include, for example, hindered amine light stabilizers, hindered phenol antioxidants, phenolic radical scavengers, sulfur antioxidants, phosphorus antioxidants, triazine compounds, benzotriazole compounds, phenolic ultraviolet absorbers, malonic acid ester ultraviolet absorbers, oxanilide ultraviolet absorbers, benzophenone compounds, and the like.

[0073] Conventionally known hindered amine light stabilizers such as hindered piperidine compounds can be used. Furthermore, the above-mentioned hindered amine light stabilizers may have particularly polymerizable unsaturated groups. Specific examples of hindered amine light stabilizers include monomer types such as bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, 4-benzoyloxy-2,2',6,6'-tetramethylpiperidine, and bis(1,2,2,6,6-pentamethyl-4-piperidyl){[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl}butylmalonate; and poly{[6-(1,1,3,3-tetramethyl]. Known examples include oligomeric types such as methylbutyl)imino-1,3,5-triazine-2,4-diyl[(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)iminol]}; polyester-bonded types such as polyesters of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and succinic acid; and those having polymerizable unsaturated groups such as 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate and 2,2,6,6-tetramethyl-4-piperidyl methacrylate.

[0074] Furthermore, commercially available hindered amine-based light stabilizers include, for example, "Tinuvin 765," "Tinuvin 770DF," "Tinuvin 144," "Tinuvin 622SF," and "Tinuvin 152" (all manufactured by BASF, trade names; Tinuvin is a registered trademark), "Adekastab LA-52," "Adekastab LA-57," "Adekastab LA-63P," "Adekastab LA-72," "Adekastab LA-77Y," "Adekastab LA-81," "Adekastab LA-82," and "Adekastab LA-87" (all manufactured by ADEKA Corporation, trade names; Adekastab and Adekastab are registered trademarks). The content of this light stabilizer can be 0.1 to 20.0% by mass, and preferably 1.0 to 10.0% by mass, relative to the total amount of the aqueous or oil-based ink composition, from the viewpoint of further light resistance and storage stability.

[0075] The writing instrument ink composition of this disclosure, configured in this manner, can be suitably applied as either aqueous or oil-based inks, and can be used as a writing instrument by being mounted on a marking pen body, a felt pen body, or a sign pen body equipped with a fiber tip, felt tip, or plastic tip at the writing end, or on a ballpoint pen body equipped with a ballpoint pen tip at the writing end. As an example of a ballpoint pen, the aqueous writing instrument ink composition of the above composition is contained in a ballpoint pen ink container (refill) equipped with a ball with a diameter of 0.18 to 2.0 mm, and an ink-following body is contained within the ink container that is incompatible with the writing instrument ink composition and has a lower specific gravity than the writing instrument ink composition, such as polybutene, silicone oil, or mineral oil. In a ballpoint pen, the axial (vertical) movement (distance) of the writing ball may be 10 to 120 μm, more preferably 15 to 100 μm, and particularly preferably 20 to 80 μm, from the standpoint of appropriately dispensing the ink composition and stabilizing the writing flow rate. This axial movement of the ball can be measured by measuring the distance between the state in which the ball is in contact with the seat of the ballpoint pen tip and the state in which the ball is in contact with the crimped part at the tip of the ballpoint pen tip, using a measuring microscope. Furthermore, the surface roughness Ra of the ball may be less than 10 nm, more preferably 1.0 to 8.0 nm. This "surface roughness Ra" can be measured using a non-contact surface shape measuring instrument (NewView 7200, Zygo) under the conditions of lens magnification 50x, evaluation length 100 μm, and Gaussian filter 25 μm, with other conditions conforming to JIS B0601 (Geometric specifications of products - surface properties).

[0076] Furthermore, if the ballpoint pen tip has a spring to bias the ball toward the tip, the spring may be nickel (Ni) plated on its surface. A bullet-shaped tip for the ballpoint pen tip is more preferable because it provides good writing performance. The structure of the ballpoint pen, marking pen, etc., is not particularly limited, and for example, it may be a direct-ink type ballpoint pen or marking pen equipped with a collector structure (ink holding mechanism) in which the barrel itself serves as the ink reservoir and the above-described writing instrument ink composition is filled into the barrel.

[0077] The ink composition and writing instrument of this disclosure contain an aqueous or oil-based ink containing an azo iron dye represented by formula (α) or formula (β) above, or a solution obtained by dissolving the azo iron dye in a solvent with a water solubility of 1% by mass or more, and further containing a solution obtained by dissolving a material having absorption at the above-mentioned specific wavelength. When writing on paper or the like with a writing instrument such as a ballpoint pen or marking pen equipped with this ink, the ink composition and writing instrument will be obtained that have blackness while also being excellent in lightfastness and storage stability.

[0078] Next, the present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples. [Examples 1-6, Comparative Examples 1-2: Aqueous Ink Compositions for Writing Instruments] Aqueous ink compositions for writing instruments were prepared with the formulations shown in Table 3 below. The azo iron dye solutions 1-5 and chromium-containing gold dye solution 1 used in these aqueous ink compositions for writing instruments were as follows. In addition, the colorants listed in Table 3 (product names, etc.) were used as colorants for Comparative Examples 1-2.

[0079] (Azo iron dye solution 1) Azo iron dye solution 1 was prepared by dissolving 15 parts of the substance represented by formula (α) as the azo iron dye component in 85 parts of ethanol, a solvent with a water solubility of 1% by mass or more. (Azo iron dye solution 2) Azo iron dye solution 2 was prepared by dissolving 15 parts of the substance represented by formula (α) as the azo iron dye component and 5 parts of Oil Yellow 129: manufactured by Orient Chemical Industry Co., Ltd. as a complementary dye in 80 parts of ethanol, a solvent with a water solubility of 1% by mass or more. (Azo iron dye solution 3) Azo iron dye solution 3 was prepared by dissolving 10 parts of the substance represented by formula (β) as the azo iron dye component in 90 parts of ethanol, a solvent with a water solubility of 1% by mass or more.

[0080] (Azo iron dye solution 4) Azo iron dye solution 2 was prepared by dissolving 10 parts of the substance represented by formula (β) as the azo iron dye component and 11085 parts of OValifast Yellow, manufactured by Orient Chemical Industry Co., Ltd., as a complementary color dye, in 85 parts of ethanol, a solvent with a water solubility of 1% by mass or more. (Azo iron dye solution 5) Azo iron dye solution 5 was prepared by dissolving 10 parts of the substance represented by formula (β) as the azo iron dye component and 10 parts of the substance represented by formula (β) as the azo iron dye component in 80 parts of ethanol, a solvent with a water solubility of 1% by mass or more. (Chromium complex dye solution 1) Chromium-containing dye solution 1 was prepared by dissolving 15 parts of VALIFASTBLACK 3830 (manufactured by Orient Chemical Industry Co., Ltd.), a mixture of azo compound chromium complex dye and amine, as the chromium complex dye component, in 85 parts of ethanol, a solvent with a water solubility of 1% by mass or more.

[0081] Using the obtained azo iron dye solutions 1 to 5 and chromium-containing dye solution 1, aqueous ink compositions for writing instruments, Examples 1 to 6 and Comparative Examples 1 to 2, were prepared by conventional methods according to the formulations shown in Table 3 below. These compositions were then applied to writing instruments (sign pens, ballpoint pens) with the following configurations, and evaluated for black color development, lightfastness, storage stability, and specified heavy metal content using the evaluation methods described below. The results are shown in Table 3 below.

[0082] (Writing instrument: Preparation of felt-tip pen) A felt-tip pen was prepared by filling the container with the water-based ink composition obtained for writing instruments using a felt-tip pen [manufactured by Mitsubishi Pencil Co., Ltd., product name: Pin, pen tip: POM resin core, cap type].

[0083] (Method for Evaluating Black Color Development) Using the writing instruments obtained above, the black color development was visually evaluated by sensory perception. For the evaluation of black, VALIFAST BLACK3810 (manufactured by Orient Chemical Industry Co., Ltd.), a chromium complex dye, was used as a comparative example. A 2cm x 2cm square was uniformly filled into Catherine paper (white, manufactured by HEIWA PAPER Co., Ltd.) by machine writing. The blackness of the ink-coated area was compared relatively. The black color development of the ink prepared using only the chromium complex dye was judged as "C", and a relative evaluation was performed according to the following criteria. Evaluation criteria: A: Significantly higher blackness than the chromium complex dye B: Slightly higher blackness than the chromium complex dye C: Blackness of the chromium complex dye

[0084] (Method for evaluating lightfastness) Using the writing instruments obtained above, Catherine paper (white, manufactured by HEIWA PAPER Co., Ltd.) with a 2cm x 2cm square filled in was used to evaluate lightfastness using a Suga Test Instruments X25 xenon weather meter under JIS L 0843 xenon arc light at 50 W / m 2 After 6 hours of irradiation with (300-400 nm) light, the visibility when exposed to a 365 nm UV lamp was evaluated based on visual inspection and the rate of change in fluorescence intensity (365 nm) according to the following evaluation criteria. Evaluation criteria: A: No change in blackness from the initial state, no problem with visibility B: Visible, but a slight change in blackness is observed C: Difficult to see, but still visible. A significant change in blackness is observed.

[0085] (Method for evaluating storage stability) Using the aqueous ink composition for writing instruments obtained above, the stability over time was evaluated by placing the aqueous ink composition in a glass mayonnaise bottle (manufactured by AS ONE Corporation) and storing it at a temperature of 60°C for a period of two weeks. After that, the aqueous ink composition for writing instruments was dropped onto filter paper (circular quantitative filter paper, No. 5C, manufactured by ADVANTEC Corporation), and the presence or absence of precipitates on the filter paper was visually evaluated according to the following evaluation criteria. Evaluation criteria: A: No precipitates B: Some precipitates observed C: Significant precipitates observed

[0086] (Evaluation of Heavy Metal Content) The presence or absence of heavy metals in each of the above azo iron dye solutions was evaluated according to the following evaluation criteria. The presence or absence of heavy metals was evaluated using high-performance liquid chromatography-intensity spectrometry (LC-ICP / MS) for the chromium compounds contained in each azo iron dye solution. The evaluation criteria were based on the heavy metal elution test, "European Standard EN71 Part 3 Migration of Specific Elements," and the amount of eluted was measured. If chromium (trivalent chromium / hexavalent chromium) exceeding the standard was detected, an elution test was conducted and a judgment was made based on the standard value (standard value after May 20, 2021, based on EN 71-3:2019 + A1:2021). Evaluation Criteria: OK: Meets the standard value Not: Does not meet the standard value

[0087] [Examples 7-12, Comparative Examples 3-4: Oil-based ink compositions for writing instruments] Using the azo iron dye solutions 1-5 and chromium-containing dye solution 1 obtained above, oil-based ink compositions for writing instruments were prepared by conventional methods according to the formulations shown in Table 4 below for Examples 7-12 and Comparative Examples 3-4.

[0088] The oil-based ink compositions for writing instruments obtained in Examples 7-12 and Comparative Examples 3-4 were used in writing instruments (ballpoint pens) with the following configurations, and their black color development, lightfastness, and storage stability were evaluated according to the evaluation methods described above. The results are shown in Table 4 below. Regarding the specified heavy metal content, the oil-based ink compositions for writing instruments used the azo iron dye solutions 1-5 described above, so the evaluation is the same as for the aqueous ink compositions for writing instruments.

[0089] (Writing instrument: Ballpoint pen preparation) Using the obtained oil-based ink composition for writing instruments, an oil-based ballpoint pen was prepared by filling the container with the above-mentioned aqueous ink compositions using a ballpoint pen [Mitsubishi Pencil Co., Ltd., product name: Uni-ball i UB-150, pen tip: metal, cap type, ball diameter: 0.5 mm].

[0090]

[0091]

[0092] As is clear from the results in Tables 3 and 4 above, the aqueous ink compositions for writing instruments of Examples 1 to 6 and the oil-based ink compositions for writing instruments of Examples 7 to 12 within the scope of this disclosure were found to be superior to Comparative Examples 1 to 4, which are outside the scope of this disclosure, in terms of lightfastness and storage stability, while maintaining blackness, even when containing black azo iron dye in the ink, regardless of whether they are aqueous or oil-based.

[0093] The ink compositions for writing instruments disclosed herein can be suitably used in aqueous ink compositions and oil-based ink compositions for writing instruments such as low-viscosity ballpoint pens, cotton-filled writing instruments and direct-ink writing instruments, gel ink ballpoint pens, cotton-filled felt-tip pens, valve-type felt-tip pens, and direct-ink felt-tip pens.

Claims

1. A writing instrument ink composition characterized by containing at least an azo iron dye represented by the following formula (α) or formula (β). [In the above formula (α), R 1 is the same or different and is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and R 2 , R 3 is the same or different and is an alkyl group having 3 to 10 carbon atoms, and A + represents a monovalent ammonium ion having an alkyl group having 3 to 18 carbon atoms or an ammonium ion of a guanidine derivative. ] [In the above formula (β), R 1 and R 2 are each independently a linear or branched alkyl group having 3 to 10 carbon atoms, R 3 is an electron-withdrawing group, R 4 is a linear or branched alkyl group having 1 to 5 carbon atoms or a linear or branched alkoxy group having 1 to 5 carbon atoms, R 5 is a nitro group, a sulfonamide group, or a halogen atom, R 6 is a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, a nitro group, or a halogen atom, R 7 is a hydrogen atom or a linear or branched alkyl group having 3 to 12 carbon atoms, and A + represents a monovalent cation. ] 2. The writing instrument ink composition according to claim 1, comprising dissolving an azo iron dye represented by formula (α) or formula (β) in a solvent having a water solubility of 1% by mass or more.

3. A writing instrument characterized by being equipped with the writing instrument ink composition described in claim 1 or 2.

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