Water-based ink composition for writing instruments and writing instruments containing the same

Abstract

The present invention provides an aqueous ink composition for writing instruments that can form white ink on a colored writing surface (especially a black writing surface), and where external force is applied, the ink becomes invisible on the writing surface, making the ink irreversibly erasable, and a writing instrument containing this ink composition. [Solution] An aqueous ink composition for writing instruments comprising a microcapsule pigment that is destroyed by the application of an external force and water, wherein the microcapsule pigment contains at least one compound selected from the group consisting of crystalline esters, ethers, and ketones, with a melting point in the range of -40 to 95°C.

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition for writing instruments and a writing instrument containing the same.

Background Art

[0002] Conventionally, a writing instrument containing an ink composition that uses titanium oxide as a colorant and can form white handwriting on a black writing surface (paper surface) is known (see, for example, Patent Document 1). In addition, a thermochromic writing instrument containing a thermochromic ink composition containing microcapsule pigments encapsulating a reversible thermochromic composition is known (see, for example, Patent Document 2). The reversible thermochromic composition in the thermochromic ink composition is colored in the coloring state and changes to a colorless state by heating. Therefore, the handwriting formed using this writing instrument changes color from colored to colorless by heating. That is, if the writing surface is white, the colorless handwriting is not visible, so the handwriting on the writing surface can be erased. On the other hand, when the writing surface is colored, the colorless handwriting may be visible as a cloudy afterimage, and the handwriting on the writing surface cannot be erased, which may impair practicality. Especially when the writing surface is black, the cloudy afterimage may be significantly visible.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention is based on the aforementioned background art and aims to provide an aqueous ink composition for writing instruments that can form white ink on a colored writing surface (particularly a black writing surface) and irreversibly erase the formed ink, and a writing instrument containing this composition. [Means for solving the problem]

[0005] To solve the above problems, the present invention provides the following embodiments. [1] A water-based ink composition for writing instruments, comprising microcapsule pigments that are destroyed by the application of an external force, and water, wherein the microcapsule pigments contain at least one compound selected from the group consisting of crystalline esters, ethers, and ketones, with a melting point in the range of -40 to 95°C. [2] The ink composition of [1] wherein the melting point of the compound is in the range of 35°C to 90°C. [3] The ink composition of [1] wherein the external force applying means is a friction member or friction body. [4] A writing instrument comprising the ink compositions [1] to [3]. [5] A writing instrument [4] comprising a friction member as the means for applying the external force. [6] A writing instrument set comprising the writing instrument [4] and the friction body as the means for applying the external force. [7] A method for using a writing instrument, characterized by using a writing instrument containing an aqueous ink composition for writing instruments, which comprises a microcapsule pigment that is destroyed by the application of an external force means and water, wherein the microcapsule pigment contains at least one compound selected from the group consisting of crystalline esters, ethers, and ketones having a melting point in the range of -40 to 95°C, to form an image on a writing surface, and then applying the external force means to the image to destroy the microcapsule pigment and erase the image. [8] A method for using the writing instrument of [7], wherein the melting point of the compound is in the range of 35°C to 90°C. [9] A method of using the writing instrument according to [7] or [8], wherein the external force applying means is a friction member or friction body. [Effects of the Invention]

[0006] The present invention provides an aqueous ink composition for writing instruments that can form white ink on a colored writing surface (particularly a black writing surface), and where external force is applied, the ink becomes invisible on the writing surface, making the ink irreversibly erasable, and a writing instrument containing this composition. [Modes for carrying out the invention]

[0007] [Water-based ink composition for writing instruments] The aqueous ink composition for writing instruments according to the present invention (hereinafter sometimes referred to as "ink composition" or "ink") comprises a microcapsule pigment that contains at least a crystalline compound selected from the group consisting of esters, ethers, and ketones (hereinafter sometimes referred to as "crystalline compound") having a melting point in the range of -40 to 95°C, and is destroyed by the application of an external force, and water. The following describes each component that constitutes the ink composition according to the present invention.

[0008] (Microencapsulated pigments) The microcapsule pigment consists of a wall film and an encapsulated substance (including a crystalline compound described later) contained within the wall film. The microcapsule pigment serves as a colorant in the ink composition according to the present invention.

[0009] ·Wall membrane The membrane forms an internal space in which the encapsulated material is contained, and this internal space is separated from the outside. As a result, the microcapsule pigment is less susceptible to external influences, and the encapsulated material is protected from various degradation factors. The membrane is destroyed by applying an external force application means, as described later. In other words, the microcapsule pigment is destroyed by the external force application means.

[0010] The material that forms the wall film (hereinafter sometimes referred to as "wall film forming material") is not particularly limited. Examples include polyurea, polyamide, polyurethane, epoxy resin, melamine resin, urea resin, urea urethane resin, isocyanate resin, vinyl resin, gelatin, ethylcellulose, polyvinyl alcohol, carboxymethylcellulose, etc. These can be used individually or in combination of two or more.

[0011] • Inclusions (crystalline compounds) Crystalline compounds are compounds selected from the group consisting of esters, ethers, and ketones, which are crystalline and have a melting point in the range of -40 to 95°C. Crystalline compounds are in a solid state (crystal) at temperatures below their freezing point, and in a liquid state where the crystal has melted at temperatures above their melting point. The following are examples of compounds that can be used in crystalline compounds. These can be used individually or in combination of two or more.

[0012] Examples of esters include: esters with a total of 13 or more carbon atoms consisting of a monocarboxylic acid and an aliphatic monohydric alcohol or a monohydric alcohol having an alicyclic ring; esters with a total of 18 or more carbon atoms consisting of an aliphatic divalent or polyvalent carboxylic acid and an aliphatic monohydric alcohol or a monohydric alcohol having an alicyclic ring; esters with a total of 18 or more carbon atoms consisting of an aliphatic divalent or polyhydric alcohol, or a divalent or polyhydric alcohol having an alicyclic ring, and a monocarboxylic acid; esters with a total of 24 or more carbon atoms consisting of an aromatic ring and a monocarboxylic acid; esters with a total of 15 or more carbon atoms consisting of an aromatic ring and an aliphatic monohydric alcohol or a monohydric alcohol having an alicyclic ring; esters with a total of 14 or more carbon atoms consisting of an aromatic ring and a monohydric alcohol having an aromatic ring; esters with a total of 15 or more carbon atoms consisting of a monocarboxylic acid and a monohydric alcohol having an aromatic ring; and esters with a total of 16 or more carbon atoms consisting of a divalent carboxylic acid and a monohydric alcohol having an aromatic ring.

[0013] Examples of esters with a total of 13 or more carbon atoms, consisting of a monocarboxylic acid and an aliphatic monohydric alcohol or a monohydric alcohol having an alicyclic ring, include pentadecyl acetate, n-tridecyl butyrate, n-pentadecyl butyrate, n-nonyl caprylate, n-undecyl caprylate, n-lauryl caprylate, n-tridecyl caprylate, n-pentadecyl caprylate, cetyl caprylate, stearyl caprylate, n-propyl caprate, n-heptyl caprate, n-undecyl caprate, n-lauryl caprate, n-tridecyl caprate, and n-pentadecyl caprate. Caprate, cetyl caprate, stearyl caprate, n-undecyl caproate, n-tridecyl caproate, n-pentadecyl caproate, n-nonyl caproate, n-undecyl caproate, stearyl caproate, n-hexyl caprylate, n-heptyl caprylate, n-octyl caprylate, methyl laurate, n-heptyl laurate, n-pentyl laurate, neopentyl laurate, 2-ethylhexyl laurate, n-octyl laurate, n-nonyl laurate, n-decyl laurate, n-undecyl laurate, lauryl laurate, n-tridecyl laurate, myristyl laurate, n-pentadecyl laurate, stearyl laurate, cyclohexylmethyl laurate, methyl myristate, n-pentyl myristate, n-heptyl myristate, n-nonyl myristate, n-decyl myristate, n-undecyl myristate, lauryl myristate, n-tridecyl myristate, myristyl myristate, n-pentadecyl myristate, cetyl myristate, stearyl myristate, cyclohexyl myristate, methyl palmitate, ethyl palmitate, palmitate n-propyl palmitate, n-pentyl palmitate, neopentyl palmitate, n-heptyl palmitate, n-nonyl palmitate, n-decyl palmitate, n-undecyl palmitate, lauryl palmitate, n-tridecyl palmitate, myristyl palmitate, n-pentadecyl palmitate, cetyl palmitate, stearyl palmitate, cyclohexylmethyl palmitate, methyl stearate, n-amyl stearate, n-heptyl stearate, neopentyl stearate, n-octyl stearate, n-nonyl stearate,n-decyl stearate, n-undecyl stearate, n-tridecyl stearate, myristyl stearate, n-pentadecyl stearate, cetyl stearate, stearyl stearate, eicosyl stearate, n-docosyl stearate, cyclohexylmethyl stearate, oleyl stearate, isostearyl stearate, cyclohexylmethyl stearate, methyl eicoate, n-amyl eicoate, n-heptyl eicoate, n-octyl eicoate, n-nonyl eicoate, Examples include n-decyl eicoate, n-undecyl eicoate, n-tridecyl eicoate, n-pentadecyl eicoate, ethyl behenate, n-amyl behenate, n-heptyl behenate, neopentyl behenate, n-octyl behenate, n-nonyl behenate, n-decyl behenate, n-undecyl behenate, n-tridecyl behenate, myristyl behenate, n-pentadecyl behenate, cetyl behenate, stearyl cyclohexylacetate, stearyl 2-cyclohexylpropionate, neopentyl octoate, etc.

[0014] Esters with a total of 18 or more carbon atoms, consisting of an aliphatic divalent or polyvalent carboxylic acid and an aliphatic monovalent alcohol or a monovalent alcohol having an alicyclic ring, include, for example, di-n-butyl sebacate, di-n-hexyl adipate, di-n-nonyl oxalate, di-n-decyl oxalate, di-n-undecyl oxalate, dilauryl oxalate, di-n-tridecyl oxalate, dimyristyl oxalate, di-n-pentadecyl oxalate, dicetyl oxalate, di-n-heptadecyl oxalate, distearyl oxalate, dilauryl malonate, di-n-tridecyl malonate, dimyristyl malonate, and malo Di-n-pentadecyl malonate, dicetyl malonate, di-n-heptadecyl malonate, distearyl malonate, di-n-nonyl succinate, di-n-decyl succinate, di-n-undecyl succinate, dilauryl succinate, di-n-tridecyl succinate, dimyristyl succinate, di-n-pentadecyl succinate, dicetyl succinate, diheptadecyl succinate, distearyl succinate, di-n-decyl glutarate, di-n-undecyl glutarate, dilauryl glutarate, di-n-tridecyl glutarate, dimyristyl glutarate, di-n-pentadecyl glutarate, dicetyl glutarate, Di-n-heptadecyl rutarate, distearyl glutarate, di-n-decyl adipic acid, di-n-undecyl adipic acid, dilauryl adipic acid, di-n-tridecyl adipic acid, dimyristyl adipic acid, di-n-pentadecyl adipic acid, dicetyl adipic acid, di-n-heptadecyl adipic acid, distearyl adipic acid, di-n-docosyl adipic acid, di-n-decyl pimephosphate, di-n-undecyl pimephosphate, dilauryl pimephosphate, di-n-tridecyl pimephosphate, dimyristyl pimephosphate, di-n-pentadecyl pimephosphate, dicetyl pimephosphate, di-n -Heptadecyl, distearyl pimelate, di-n-decyl suberate, di-n-undecyl suberate, dilauryl suberate, di-n-tridecyl suberate, dimyristyl suberate, di-n-nonyl sebacate, di-n-decyl sebacate, di-n-undecyl sebacate, dilauryl sebacate, di-n-tridecyl sebacate, dimyristyl sebacate, di-n-pentadecyl sebacate, dicetyl sebacate, di-n-heptadecyl sebacate, distearyl sebacate, di-n-pentadecyl suberate, dicetyl suberate, di-n-heptadecyl suberate,Examples include distearyl suberate, di-n-decyl azelaate, di-n-undecyl azelaate, dilauryl azelaate, di-n-tridecyl azelaate, dimyristyl azelaate, di-n-pentadecyl azelaate, dicetyl azelaate, di-n-heptadecyl azelaate, distearyl azelaate, di-n-octyl 1,18-octadecylmethylenedicarboxylic acid, dicyclohexyl 1,18-octadecylmethylenedicarboxylic acid, and dineopentyl 1,18-octadecylmethylenedicarboxylic acid.

[0015] Examples of esters with a total of 18 or more carbon atoms, consisting of an aliphatic divalent or polyhydric alcohol, or a divalent or polyhydric alcohol having an alicyclic ring, and a monovalent carboxylic acid, include ethylene glycol dicaprylate, ethylene glycol dicaprate, ethylene glycol diundecanoate, ethylene glycol dilaurate, ethylene glycol ditridecanoate, ethylene glycol dimyristate, ethylene glycol dipentadecanate, ethylene glycol dipalmitate, and ethylene glycol dipalmitate. Licor diheptadecanoate, ethylene glycol distearate, 1,3-propanediol dicaprylate, 1,3-propanediol dicaprate, 1,3-propanediol diundecanoate, 1,3-propanediol dilaurate, 1,3-propanediol ditridecanoate, 1,3-propanediol dimyristate, 1,3-propanediol dipentadecanoate, 1,3-propanediol dipalmitate, 1,3-propanediol diheptadecanoate Stel, 1,3-propanediol distearate, 1,4-butanediol dicaprylate, 1,4-butanediol dicaprate, 1,4-butanediol diundecanoate, 1,4-butanediol dilaurate, 1,4-butanediol ditridecanoate, 1,4-butanediol dimyristate, 1,4-butanediol dipentadecanoate, 1,4-butanediol dipalmitate, 1,4-butanediol diheptadecanoate, 1,4-butanediol distearate Phosphate ester, 1,5-pentanediol dicaprate, 1,5-pentanediol diundecanoate, 1,5-pentanediol dilaurate, 1,5-pentanediol ditridecanoate, 1,5-pentanediol dimyristate, 1,5-pentanediol dipentadecanoate, 1,5-pentanediol dipalmitate, 1,5-pentanediol diheptadecanoate, 1,5-pentanediol distearate, 1,6-hexanediol dicaprate, 1,6-Hexanediol diundecanoate, 1,6-Hexanediol dilaurate, 1,6-Hexanediol ditridecanoate, 1,6-Hexanediol dimyristate, 1,6-Hexanediol dipentadecanoate, 1,6-Hexanediol dipalmitate, 1,6-Hexanediol diheptadecanoate, 1,6-Hexanediol distearate, 1,7-Pentanediol dicaprate, 1,7-Pentanediol diundecanoate, 1,7-Pentanediol Ludilaurate, 1,7-pentanediol ditridecanoate, 1,7-pentanediol dimyristate, 1,7-pentanediol dipentadecanoate, 1,7-pentanediol dipalmitate, 1,7-pentanediol diheptadecanoate, 1,7-pentanediol distearate, 1,8-octanediol dicaprate, 1,8-octanediol diundecanoate, 1,8-octanediol dilaurate, 1,8-octanediol ditridecanoate 1,8-octanediol dimyristate, 1,8-octanediol dipentadecanoate, 1,8-octanediol dipalmitate, 1,8-octanediol diheptadecanoate, 1,8-octanediol distearate, 1,9-nonanediol dicaprate, 1,9-nonanediol diundecanoate, 1,9-nonanediol dilaurate, 1,9-nonanediol ditridecanoate, 1,9-nonanediol dimyristate, 1,9-nonanediol di Pentadecanoate, 1,9-nonanediol dipalmitate, 1,9-nonanediol diheptadecanoate, 1,9-nonanediol distearate, 1,10-decanediol dicaprylate, 1,10-decanediol dicaprate, 1,10-decanediol diundecanoate, 1,10-decanediol dilaurate, 1,10-decanediol ditridecanoate, 1,10-decanediol dimyristate, 1,10-decanediol dipentadecanoate, 1,Examples thereof include 10-decanediol dipalmitate, 1,10-decanediol diheptadecanoate, 1,10-decanediol distearate, 1,5-pentanediol distearate, 1,2,6-hexanetriol dimyristate, pentaerythritol trimyristate, pentaerythritol tetralaurate, 1,4-cyclohexanediol dimyristyl, 1,4-cyclohexanediol didecyl, 1,4-cyclohexanediol dimyristyl, 1,4-cyclohexanediol distearyl, dilaurate of 1,4-cyclohexanedimethanol, dimyristate of 1,4-cyclohexanedimethanol, etc.

[0016] Examples of esters having 24 or more carbon atoms in total, composed of a divalent alcohol having an aromatic ring and a monovalent carboxylic acid, include, for example, xylylene glycol dicaprylate, xylylene glycol dicaprate, xylylene glycol diundecanoate, xylylene glycol dilaurate, xylylene glycol ditridecanoate, xylylene glycol dimyristate, xylylene glycol dipentadecanoate, xylylene glycol dipalmitate, xylylene glycol diheptadecanoate, xylylene glycol distearate, etc.

[0017] Esters with a total of 15 or more carbon atoms, consisting of a monocarboxylic acid having an aromatic ring and an aliphatic monohydric alcohol or a monohydric alcohol having an alicyclic ring, include, for example, hexyl dimethylbenzoate, decyl methylbenzoate, lauryl methylbenzoate, myristyl methylbenzoate, stearyl methylbenzoate, cetyl tert-butylbenzoate, behenyl cyclohexylbenzoate, myristyl phenylbenzoate, lauryl octylbenzoate, stearyl ethylbenzoate, decyl 4-isopropylbenzoate, stearyl benzoylbenzoate, stearyl chlorobenzoate, myristyl bromobenzoate, stearyl 2-chloro-4-bromobenzoate, and 3,4 Examples include decyl dichlorobenzoate, octyl 2,4-dibromobenzoate, cetyl 3-nitrobenzoate, cyclohexylmethyl 4-aminobenzoate, cetyl 4-diethylaminobenzoate, stearyl 4-anilinobenzoate, decyl 4-methoxybenzoate, cetyl 4-methoxybenzoate, octyl 4-butoxybenzoate, cetyl 4-hydroxybenzoate, stearyl p-chlorophenyl acetate, cetyl p-chlorophenyl acetate, neopentyl salicylate, stearyl 2-naphthoate, cetyl benzylate, stearyl benzylate, decyl 3-benzoylpropionate, stearyl benzoate, myristyl benzoate, cyclohexylmethyl 2-benzoylpropionate, and cyclohexylmethyl cinnamate.

[0018] Examples of esters with a total of 14 or more carbon atoms, consisting of a monocarboxylic acid having an aromatic ring and a monohydric alcohol having an aromatic ring, include benzyl salicylate, 4-methoxymethylphenylmethyl salicylate, 4-chlorophenylmethyl benzoate, benzyl cinnamate, 4-tert-butylbenzoate phenyl, 2-methylbenzoate 4-chlorobenzyl, and 4-methoxyphenylmethyl benzoate.

[0019] Examples of esters with a total of 15 or more carbon atoms, consisting of a monovalent carboxylic acid and a monovalent alcohol having an aromatic ring, include 4-chlorophenylmethyl caprylate, 4-chlorophenylmethyl caprate, 4-methoxyphenylmethyl laurate, 4-methoxyphenylmethyl myristate, 4-nitrophenylmethyl stearate, 4-methylphenylmethyl caprate, 2-chlorophenylmethyl myristate, 4-chlorophenyl 11-bromolaurate, 4-isopropylphenyl stearate, stearyl 2-naphthoate, cetyl benzylate, stearyl benzylate, benzyl caproate, benzyl palmitate, 3-phenylpropyl stearate, and phenyl 11-bromolaurate.

[0020] Examples of esters with a total of 16 or more carbon atoms, consisting of a divalent carboxylic acid and a monohydric alcohol having an aromatic ring, include dibenzyl sebacate and 4,4′-diphenyldicarboxylic acid dineopentyl.

[0021] Furthermore, the esters may be compounds represented by the following formula (1). [ka] [In the formula, R1 represents a hydrogen atom or a methyl group, m represents an integer from 0 to 2, and either X1 or X2 is -(CH2)] n OCOR2 or (CH2) n COOR2, the other side represents a hydrogen atom, n is an integer from 0 to 2, R2 represents an alkyl or alkenyl group with 4 or more carbon atoms, Y1 and Y2 each independently represent one of the following: a hydrogen atom, an alkyl group with 1 to 4 carbon atoms, a methoxy group, or a halogen atom, and r and p each independently represent an integer from 1 to 3. Specifically, examples of compounds represented by formula (1) include the compounds shown in formula (2) below. [ka] (In the formula, R represents an alkyl or alkenyl group having 8 or more carbon atoms, preferably an alkyl group having 10 to 24 carbon atoms, and more preferably an alkyl group having 12 to 22 carbon atoms.) Examples of compounds represented by formula (2) include 4-benzyloxyphenylethyl octanoate, 4-benzyloxyphenylethyl nonanoate, 4-benzyloxyphenylethyl decanoate, 4-benzyloxyphenylethyl undecanoate, 4-benzyloxyphenylethyl dodecanoate, 4-benzyloxyphenylethyl tridecanoate, 4-benzyloxyphenylethyl tetradecanoate, 4-benzyloxyphenylethyl pentadecanoate, 4-benzyloxyphenylethyl hexadecanoate, 4-benzyloxyphenylethyl heptadecanoate, and 4-benzyloxyphenylethyl octadecanoate.

[0022] Furthermore, the compound may also be represented by the following formula (3). [ka] (In the formula, R represents an alkyl or alkenyl group having 8 or more carbon atoms, m and n each independently represent an integer from 1 to 3, and X and Y each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom.) Examples of compounds represented by formula (3) include 1,1-diphenylmethyl octanoate, 1,1-diphenylmethyl nonanoate, 1,1-diphenylmethyl decanoate, 1,1-diphenylmethyl undecanoate, 1,1-diphenylmethyl dodecanoate, 1,1-diphenylmethyl tridecanoate, 1,1-diphenylmethyl tetradecanoate, 1,1-diphenylmethyl pentadecanoate, 1,1-diphenylmethyl hexadecanoate, 1,1-diphenylmethyl heptadecanoate, and 1,1-diphenylmethyl octadecanoate.

[0023] Furthermore, the compound may also be the compound shown in formula (4) below. [ka] (In the formula, X represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a halogen atom; m represents an integer from 1 to 3; and n represents an integer from 1 to 20.) Examples of compounds represented by formula (4) include diesters of malonic acid and 2-[4-(4-chlorobenzyloxy)phenyl]ethanol, diesters of succinic acid and 2-(4-benzyloxyphenyl)ethanol, diesters of succinic acid and 2-[4-(3-methylbenzyloxy)phenyl]ethanol, diesters of glutaric acid and 2-(4-benzyloxyphenyl)ethanol, diesters of glutaric acid and 2-[4-(4-chlorobenzyloxy)phenyl]ethanol, diesters of adipic acid and 2-(4-benzyloxyphenyl)ethanol, diesters of pimelic acid and 2-(4-benzyloxyphenyl)ethanol, diesters of suberic acid and 2-(4-benzyloxyphenyl)ethanol, and suberic acid and 2-[4-(3-methylbenzyloxy)phenyl]ethanol. Examples include diesters of rubenzyloxy)phenyl]ethanol, suberic acid and 2-[4-(4-chlorobenzyloxy)phenyl]ethanol, suberic acid and 2-[4-(2,4-dichlorobenzyloxy)phenyl]ethanol, azelaic acid and 2-(4-benzyloxyphenyl)ethanol, sebacic acid and 2-(4-benzyloxyphenyl)ethanol, 1,10-decanedicarboxylic acid and 2-(4-benzyloxyphenyl)ethanol, 1,18-octadecanedicarboxylic acid and 2-(4-benzyloxyphenyl)ethanol, and 1,18-octadecanedicarboxylic acid and 2-[4-(2-methylbenzyloxy)phenyl]ethanol.

[0024] Furthermore, the compound may also be the compound shown in formula (5) below. [ka] (In the formula, R represents an alkyl or alkenyl group having 1 to 21 carbon atoms, and n represents an integer from 1 to 3.) Examples of compounds represented by formula (5) include: diesters of 1,3-bis(2-hydroxyethoxy)benzene and capric acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and undecanoic acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and lauric acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and myristic acid, diesters of 1,4-bis(hydroxymethoxy)benzene and butyric acid, diesters of 1,4-bis(hydroxymethoxy)benzene and isovaleric acid, and diesters of 1,4-bis(2-hydroxyethoxy)benzene and acetic acid. Examples include diesters of 1,4-bis(2-hydroxyethoxy)benzene with propionic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene with valeric acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene with caproic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene with caprylic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene with capric acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene with lauric acid, and diesters of 1,4-bis(2-hydroxyethoxy)benzene with myristic acid.

[0025] Furthermore, the compound may also be the compound represented by the following formula (6). [ka] (In the formula, X represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom; m represents an integer from 1 to 3; and n represents an integer from 1 to 20.) Examples of compounds represented by formula (6) include diesters of succinic acid and 2-phenoxyethanol, diesters of suberic acid and 2-phenoxyethanol, diesters of sebacic acid and 2-phenoxyethanol, diesters of 1,10-decanedicarboxylic acid and 2-phenoxyethanol, and diesters of 1,18-octadecanedicarboxylic acid and 2-phenoxyethanol.

[0026] Furthermore, the compound may also be represented by the formula (7) below. [ka] (In the formula, R represents any of the following: an alkyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, a cycloalkyl group, or an alkenyl group having 4 to 22 carbon atoms; X represents any of the following: a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom; and n represents 0 or 1.) Examples of compounds represented by formula (7) include decyl phenylbenzoate, lauryl phenylbenzoate, myristyl phenylbenzoate, cyclohexylethyl phenylbenzoate, octyl 4-biphenylacetate, nonyl 4-biphenylacetate, decyl 4-biphenylacetate, lauryl 4-biphenylacetate, myristyl 4-biphenylacetate, tridecyl 4-biphenylacetate, pentadecyl 4-biphenylacetate, cetyl 4-biphenylacetate, cyclopentyl 4-biphenylacetate, cyclohexylmethyl 4-biphenylacetate, hexyl 4-biphenylacetate, and cyclohexylmethyl 4-biphenylacetate.

[0027] Furthermore, the compound may also be represented by the formula (8) below. [ka] (In the formula, R represents an alkyl group having 3 to 18 carbon atoms or an aliphatic acyl group having 3 to 18 carbon atoms; X represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or a halogen atom; Y represents a hydrogen atom or a methyl group; and Z represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or a halogen atom.) Examples of compounds represented by formula (8) include phenoxyethyl 4-butoxybenzoate, phenoxyethyl 4-pentyloxybenzoate, phenoxyethyl 4-tetradecyloxybenzoate, esters of phenoxyethyl 4-hydroxybenzoate and dodecanoic acid, and dodecyl ether of phenoxyethyl vanillate.

[0028] Furthermore, the compound may also be represented by the formula (9) below. [ka] (In the formula, R represents any of the following: an alkyl group having 4 to 22 carbon atoms, an alkenyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, or a cycloalkyl group; X represents any of the following: a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; Y represents any of the following: a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; and n represents 0 or 1.) Examples of compounds represented by formula (9) include benzoic acid esters of octyl 4-hydroxybenzoate, decyl 4-hydroxybenzoate, 4-methoxybenzoic acid ester of heptyl 4-hydroxybenzoate, 2-methoxybenzoic acid ester of dodecyl 4-hydroxybenzoate, and cyclohexylmethyl 4-hydroxybenzoate.

[0029] Furthermore, the compound may also be represented by the formula (10) below. [ka] (In the formula, R represents any of the following: an alkyl group having 3 to 18 carbon atoms, a cycloalkylalkyl group having 6 to 11 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, or an alkenyl group having 3 to 18 carbon atoms; X represents any of the following: a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, or a halogen atom; and Y represents any of the following: a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, an ethoxy group, or a halogen atom.) Examples of compounds represented by formula (10) include phenoxyethyl ether of nonyl 4-hydroxybenzoate, phenoxyethyl ether of decyl 4-hydroxybenzoate, phenoxyethyl ether of undecyl 4-hydroxybenzoate, and phenoxyethyl ether of dodecyl vanillate.

[0030] Furthermore, the compound may also be represented by the formula (11) below. [ka] (In the formula, R represents a cycloalkyl group having 3 to 8 carbon atoms or a cycloalkylalkyl group having 4 to 9 carbon atoms, and n represents an integer from 1 to 3.) Examples of compounds represented by formula (11) include diesters of 1,3-bis(2-hydroxyethoxy)benzene and cyclohexanecarboxylic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and cyclohexanepropionic acid, and diesters of 1,3-bis(2-hydroxyethoxy)benzene and cyclohexanepropionic acid.

[0031] Furthermore, the compound may also be represented by the formula (12) below. [ka] (In the formula, R represents one of the alkyl groups having 3 to 17 carbon atoms, cycloalkyl groups having 3 to 8 carbon atoms, or cycloalkylalkyl groups having 5 to 8 carbon atoms; X represents one of the hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a methoxy group, an ethoxy group, or a halogen atom; and n represents an integer from 1 to 3.) Examples of compounds represented by formula (12) include diesters of 4-phenylphenol ethylene glycol ether and cyclohexanecarboxylic acid, diesters of 4-phenylphenol diethylene glycol ether and lauric acid, diesters of 4-phenylphenol triethylene glycol ether and cyclohexanecarboxylic acid, diesters of 4-phenylphenol ethylene glycol ether and octanoic acid, diesters of 4-phenylphenol ethylene glycol ether and nonanoic acid, diesters of 4-phenylphenol ethylene glycol ether and decanoic acid, and diesters of 4-phenylphenol ethylene glycol ether and myristic acid.

[0032] Examples of ethers include aliphatic ethers with a total of 16 or more carbon atoms, and ethers having aromatic rings with a total of 11 or more carbon atoms.

[0033] Examples of aliphatic ethers with a total of 16 or more carbon atoms include dioctyl ether, diethylhexyl ether, didecyl ether, didodecyl ether, ditridecyl ether, ditetradecyl ether, dipentadecyl ether, dihexadecyl ether, diheptadecyl ether, and dioctadecyl ether.

[0034] Examples of ethers having aromatic rings with a total of 11 or more carbon atoms include benzyl isoamyl ether, diphenyl ether, ethylene glycol diphenyl ether, and diisopropyl benzyl ether.

[0035] Examples of ketones include aliphatic ketones with 10 or more total carbon atoms, and ketones having an aromatic ring or alicyclic ring with 10 or more total carbon atoms.

[0036] Examples of aliphatic ketones with a total of 10 or more carbon atoms include 2-decanone, 3-decanone, 4-decanone, 2-undecanone, 3-undecanone, 4-undecanone, 5-undecanone, 6-undecanone, 2-dodecanone, 3-dodecanone, 4-dodecanone, 5-dodecanone, 2-tridecanone, 3-tridecanone, 2-tetradecanone, 2-pentadecanone, 8-pentadecanone, 2-hexadecanone, 3-hexadecanone, 9-heptadecanone, 2-pentadecanone, 2-octadecanone, 2-nonadecanone, 10-nonadecanone, 2-eicosanone, 11-heneicosanone, 2-docosanone, laurone, stearone, and cyclodecanone.

[0037] Examples of ketones having an aromatic ring or alicyclic ring with a total of 10 or more carbon atoms include benzylacetophenone, benzylphenylketone, n-octadecanophenone, n-heptadecanophenone, n-hexadecanophenone, n-tetradecanophenone, n-tridecanophenone, laurophenone, n-undecanophenone, n-decanophenone, 4′-n-octylacetophenone, n-nonanophenone, 4′-n-heptylacetophenone, n-octanophenone, 4′-n-hexylacetophenone, 4′-cyclohexylacetophenone, and 2-methylbe Benzophenone, dicyclohexyl ketone, 4-tert-butylpropiophenone, n-heptanophenone, 4′-n-pentylacetophenone, cyclohexylphenyl ketone, 2-benzylidenecyclohexanone, benzophenone, cyclodecanone, 2-n-heptylcyclohexanone, 2-cyclohexylcyclohexanone, 2-(1-cyclohexyl)cyclohexanone, benzyl n-butyl ketone, 4′-n-butylacetophenone, n-hexanophenone, 4-isobutylacetophenone, cyclopentylphenyl ketone, 4-phenylcyclo Rohexanone, 1-acetophthalone, 2-acetophthalone, 4-n-pentylcyclohexanone, benzylisopropyl ketone, 4'-n-propylacetophenone, 2',4',6'-trimethylacetophenone, cyclobutylphenyl ketone, 2',4'-dimethylacetophenone, 2',5'-dimethylacetophenone, 4'-ethylacetophenone, isopropylphenyl ketone, 4'-methylpropiophenone, 1-phenyl-2-butanone, phenyl n-propioketone, cyclopropylphenyl ketone, phenylpropenyl ketone, 2 -amino-4′-chlorobenzophenone, 2-amino-5-chlorobenzophenone, 4-fluorobenzophenone, 2-amino-2′,5-chlorobenzophenone, 4-chloro-4′-hydroxybenzophenone, 2-chlorobenzophenone, 4-chlorobenzophenone, 2,4′-difluorobenzophenone, 4,4′-difluorobenzophenone, 2,4-dichlorobenzophenone, 2,4′-dichlorobenzophenone, 4,4′-dichlorobenzophenone, 2,3,4,5,6-pentafluorobenzophenone, decafluorobenzophenone, 3,Examples include 3′-diaminobenzophenone, 3,4-diaminobenzophenone, 4,4′-diaminobenzophenone, 2-aminobenzophenone, 4-aminobenzophenone, 3,4-dimethoxyphenyl cysetone, 2′,3′,4′-trimethoxyacetophenone, 3′,4′,5′-trimethoxyacetophenone, etc.

[0038] • Additives Microcapsule pigments may contain other components besides the aforementioned crystalline compounds selected from the group consisting of esters, ethers, and ketones with melting points in the range of -40 to 95°C, as long as they do not affect their function. Examples of other components include various additives such as antioxidants, ultraviolet absorbers, infrared absorbers, preservatives, or fungicides.

[0039] Microencapsulated pigments are obtained by known microencapsulation methods. Examples of microencapsulation methods include interfacial polymerization, in situ polymerization, liquid curing and coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension and coating, and spray drying, and are selected as appropriate depending on the application.

[0040] For example, microcapsule pigments can be obtained using interfacial polymerization as follows. First, an emulsion is prepared by adding a system (oil phase) containing the encapsulation material and the wall material to an aqueous medium (aqueous phase) all at once or in stages and stirring. As stirring continues, the wall material polymerizes at the interface between the oil phase and the aqueous phase (interfacial polymerization reaction). At this time, the wall closes to hold the encapsulation material inside, forming a microcapsule. Finally, the microcapsules are separated from the aqueous phase, washed, and dried to isolate the microcapsule pigment.

[0041] A curing agent may be added to the reaction system. The reaction system may be heated. Desolvent removal may be performed during or after the interfacial polymerization reaction.

[0042] Microcapsule pigments that are destroyed by the application of an external force can be prepared, for example, by reducing the thickness of the wall film of the microcapsule pigment.

[0043] The mass ratio of microcapsule pigment, encapsulated material, and wall film is preferably 7:1 to 3:1, and more preferably 6:1 to 3:1. When the mass ratio of encapsulated material to wall film is within the above range, the density of the white color of the writing produced by a writing instrument containing the ink composition according to the present invention is excellent, and the microcapsule pigment can be easily destroyed by applying an external force.

[0044] The average particle size of the microcapsule pigment is preferably in the range of 0.01 to 5 μm, more preferably 0.1 to 3 μm, and even more preferably 0.5 to 3 μm. If the average particle size exceeds 5 μm, it becomes difficult to obtain good ink discharge from writing instruments. On the other hand, if the average particle size is less than 0.01 μm, it becomes difficult to exhibit high-concentration color development.

[0045] <Method for calculating average particle size> The average particle size of the microcapsule pigment is the equivalent diameter of an isovolume sphere, measured using a laser diffraction / scattering particle size distribution analyzer (e.g., LA-960V2, manufactured by Horiba, Ltd.) that has undergone a predetermined calibration. The average particle size is the average value of the equivalent diameter of an equal-volume sphere (the particle size D50, i.e., the median diameter, which corresponds to a frequency of 50% when the particle size distribution is determined based on volume).

[0046] The prescribed calibration will be explained. If the particle size of all microcapsules exceeds 0.20 μm, the average value of the equivalent diameter of equivolute spheres is measured using the Coulter method with a particle size distribution analyzer (e.g., Multisizer 4e, manufactured by Beckman Coulter, Inc.), and calibration is performed based on that value.

[0047] In cases other than those described above, the microcapsule region is determined using image analysis-based particle size distribution measurement software (for example, MacView, manufactured by Mountec Co., Ltd.), the projected area equivalent diameter (Heywood diameter) is calculated from the area of ​​the microcapsule region, and calibration is performed based on the average value of these equivalent diameters of equivolute spheres.

[0048] The writing produced by the ink composition according to the present invention is white. This whiteness is thought to be due to the reflection (i.e., scattering) of visible light in various directions from the outer surface of the microcapsule pigment. Therefore, since the microcapsule pigment according to the present invention is itself white, it can be used as a colorant. White writing can be produced using the microcapsule pigment according to the present invention. The crystalline compound encapsulated in the microcapsule pigment may be in a solid (crystalline) state or a liquid state. Visible light is reflected from the outer surface of the microcapsule pigment, while some of the visible light passes through the wall film and enters the interior of the microcapsule pigment. If the crystalline compound is in a solid state, the visible light that enters the interior of the microcapsule pigment is also scattered on the surface of the crystalline compound, resulting in a stronger white color.

[0049] ·External force application means The writing marks formed on the writing surface can be irreversibly erased by applying an external force to destroy the microcapsule pigment. The microcapsule pigment can be destroyed by puncture or pressure. The means of applying external force is not particularly limited, as long as it can destroy the microcapsule pigment. It may be an article with a sharp part (e.g., a needle or awl), or it may be a finger or fingernail. Here, if the crystalline compound encapsulated in the microcapsule pigment is in a liquid state, applying an external force will break the microcapsule pigment, causing the liquid encapsulated substance (crystalline compound) to dissolve to the outside of the microcapsule pigment and penetrate the writing surface (paper). As a result, the handwriting in the area where the external force was applied becomes invisible and is erased. On the other hand, if the crystalline compound encapsulated in the microcapsule pigment is in a solid state (crystal), applying an external force will cause the handwriting to be rubbed using a friction member or friction body that generates frictional heat. At the same time, the microcapsule pigment is broken, and the encapsulated crystalline compound is heated by the frictional heat generated by the rubbing, becoming liquid. The crystalline compound then dissolves to the outside of the microcapsule pigment and penetrates the writing surface (paper). As a result, the handwriting in the area where the external force was applied becomes invisible and is erased. In other words, from the viewpoint of improving the density of the whiteness of the handwriting, the ink composition according to the present invention preferably has a crystalline compound in a solid state (i.e., a melting point above room temperature), and it is preferable to use a friction member or friction body as an external force application means to make the handwriting formed by such an ink composition irreversibly invisible. Here, "room temperature" is based on 20°C ± 15°C as defined in JIS Z 8703, and "room temperature range" is the temperature range of 5 to 35°C. That is, "temperature above room temperature" is a temperature above 35°C. The "friction element" is provided in the writing instrument described later and is used to rub away the writing. The "friction body" is a separate component from the writing instrument and is used to rub away the writing.

[0050] The melting point of the crystalline compound is preferably in the range of 35°C to 90°C, and more preferably in the range of 40°C to 80°C (40 to 80°C). Having the melting point within this range allows for a further improvement in the density of the white color of the handwriting. Furthermore, since the crystalline compound is easily brought into a liquid state by external force application means (especially friction members and friction bodies), when the handwriting is rubbed and the microcapsule pigment is destroyed, the crystalline compound penetrates the paper surface more easily, making it easier to reliably render the handwriting in the rubbed area invisible.

[0051] It is possible to rewrite and re-create handwriting in areas where handwriting has been erased. Similarly, by applying an external force to the handwriting, it is possible to make the handwriting irreversibly invisible. In other words, writing and erasing can be repeatedly performed on the same writing surface (paper).

[0052] The friction member or friction body is not particularly limited as long as it generates frictional heat when it rubs over the writing. For example, it may be plastic, foam, stone, metal, cloth, etc. Elastic materials such as elastomers and plastic foams that are highly elastic and generate appropriate friction when rubbed are preferred. Although a general eraser can be used as the friction body, eraser residue is generated when rubbing, so the above-mentioned friction member or friction body that generates almost no eraser residue is preferred. Examples of materials include silicone resin and styrene-ethylene-butadiene-styrene block copolymer (SEBS resin).

[0053] The content of microcapsule pigments is not particularly limited. It is preferably in the range of 5 to 40% by mass of the ink composition, and more preferably in the range of 10 to 30% by mass. By having the content within the above range, it becomes easier to achieve both the ink discharge performance and the density of the writing line of the writing instrument containing the ink composition.

[0054] Since the microcapsule pigments are white, when the writing instrument according to the present invention is used on a colored writing surface, it is possible to form a highly opaque white writing mark on the writing surface. Furthermore, by writing on or applying the ink composition according to the present invention onto a colored image (excluding white) (e.g., letters) formed on a white writing surface, the image formed on the writing surface can be concealed. Then, by applying an external force application means to the area where the ink composition has been written or applied, the concealed area can be made to reappear. Such ink compositions can be applied to correction tools. Specifically, when writing on a white writing surface (paper) with a regular black ballpoint pen, if an error occurs, the ink composition can be applied to the error using a correction tool to conceal the mistake. Then, the correct characters can be written over the concealed area with a black ballpoint pen. Furthermore, if the ink composition is unintentionally applied to an area that does not need correction when concealing an error, the unwanted concealed portion can be removed by applying an external force to that area, thereby making the unintentionally concealed area reappear. The ink composition according to the present invention can also be used for memorization purposes. Specifically, memorization can be performed by applying the ink composition to the parts of the characters that need to be memorized that are formed on a white writing surface, thereby concealing them. When it is necessary to reconfirm the content of the parts that have been concealed by the ink composition, or when memorization is complete and it is no longer necessary to conceal the parts that need to be memorized, the concealed parts can be erased by applying an external force application means to the concealed parts, thereby making those parts reappear.

[0055] (water) There are no particular restrictions on the type of water used. Examples include tap water, deionized water, ultrafiltered water, and distilled water.

[0056] (Additives) The ink composition may contain various additives. Examples of additives include water-soluble organic solvents, shear viscosity reducers, polymer flocculants, dispersants, water-soluble resins, specific gravity adjusters, surfactants, pH adjusters, resin particles, rust inhibitors, wetting agents, viscosity modifiers, preservatives or antifungal agents, foam absorbers, defoamers, antioxidants, UV absorbers, lubricants, and the like. These additives can be selected from those conventionally used in water-based inks and used as appropriate.

[0057] The ink composition can be manufactured by any conventionally known method. Specifically, the ink composition can be manufactured by mixing the required amounts of each of the above-mentioned components and stirring them with various agitators such as propeller agitators, homodispersers, or homomixers, or by dispersing them with various dispersers such as bead mills.

[0058] [Writing instruments] Examples of writing instruments that contain ink for writing instruments include various writing instruments such as ballpoint pens, marking pens, fountain pens, brush pens, and calligraphy pens.

[0059] (Ballpoint pen) When writing instrument ink is used in a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited. For example, it may be used by filling a ballpoint pen refill or ballpoint pen that includes a ballpoint pen tip and an ink filling mechanism.

[0060] A ballpoint pen tip consists of a tip body and a ball provided at the front end of the tip body. Examples of ballpoint pen tips include a tip in which a ball is held in a ball-holding portion formed by pressing the tip area of ​​a tip body made of a metal pipe inward from the outer surface; a tip in which a ball is held in a ball-holding portion formed by cutting a metal tip body with a drill or the like; a tip in which a resin ball seat is provided inside a metal or plastic tip body; or a tip in which the ball held in the tip is biased forward by a spring. The material of the tip body and ball is not particularly limited, and examples include cemented carbide, stainless steel, ruby, ceramic, resin, rubber, etc. Furthermore, the ball may be subjected to surface treatment such as DLC coating. The diameter of the ball is generally 0.1 to 3 mm, with 0.1 to 2 mm, 0.2 to 2 mm, 0.2 to 1.5 mm, 0.2 to 1.2 mm, 0.2 to 1 mm, and 0.25 to 1 mm being preferred in that order. Furthermore, the ballpoint pen tip can be configured to have a resilient member inside the tip that springs the rear end of the ball forward, so that when not writing, the ball is pressed against the inner edge of the tip, creating a tight seal, and when writing, the pressure of writing causes the ball to retract, allowing ink to flow out, thereby suppressing ink leakage when not in use. Examples of resilient members include metal thin wire springs, springs with a straight section (rod section) at one end, and linear plastic processed bodies, and they are configured and applied so as to be able to press with a resilient force of 5 to 40 g.

[0061] The ink filling mechanism is not particularly limited; for example, an ink container capable of being filled with ink can be used. As the ink container, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body can be used. In addition, to prevent the ink being degraded by oxygen, a molded body made of a resin with low oxygen permeability can also be used. Examples of resins with low oxygen permeability include ethylene-vinyl alcohol copolymer, polyvinylidene chloride, acrylonitrile resin, and polyester. The ink container may have a single-layer structure or a multi-layer structure.

[0062] A ballpoint pen refill (hereinafter sometimes referred to as "refill") can be formed by directly connecting a ballpoint pen tip to an ink reservoir or via a connecting member, and by directly filling the ink reservoir with ink. A ballpoint pen can be formed by housing this refill inside the barrel.

[0063] An ink backflow prevention device is packed into the trailing end of the ink that is filled into the ink container. Examples of ink backflow prevention devices include liquid stoppers and solid stoppers. The stopper consists of a non-volatile liquid and / or a low-volatility liquid, such as petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or co-oligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc. These can be used individually or in combination of two or more. Examples of solid stoppers include those made of polyethylene, polypropylene, polymethylpentene, and the like. A liquid stopper and a solid stopper can also be used in combination as an ink backflow prevention device.

[0064] For non-volatile and / or low-volatile liquids, it is preferable to add a thickening agent to increase the viscosity to a suitable level. Examples of thickening agents include clay-based thickeners such as silica with a hydrophobic surface treatment, fine silica particles with a methylated surface treatment, aluminum silicate, swellable mica, hydrophobic bentonite and montmorillonite; fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate; dextrin compounds such as tripenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, and fatty acid dextrins; and cellulose compounds.

[0065] By using the barrel itself as the ink filling mechanism, directly filling the barrel with ink, and attaching a ballpoint pen tip to the front end of the barrel, a ballpoint pen equipped with both a ballpoint pen tip and an ink filling mechanism can be formed.

[0066] If the ink to be filled into the ink filling mechanism is of low viscosity, a ballpoint pen comprising a ballpoint pen tip and an ink filling mechanism may further include an ink supply mechanism for supplying the ink to be filled into the ink filling mechanism to the pen tip.

[0067] The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that uses an ink guide core made of a fiber bundle or the like as an ink flow rate regulator to supply ink to the pen tip; (2) a mechanism that uses a comb-shaped ink flow rate regulator to supply ink to the pen tip; and (3) a mechanism in which a number of discs are arranged in parallel with comb-shaped spacing, and a slit-shaped ink guide groove that penetrates the discs axially and a ventilation groove wider than the groove are provided, and an ink guide core for guiding ink from the ink filling mechanism to the pen tip is positioned at the axis to supply ink to the pen tip via a pen core.

[0068] The material of the pen tip is not particularly limited as long as it is a synthetic resin that can be injection molded into a structure with numerous disc-shaped grooves. Acrylonitrile-butadiene-styrene copolymer (ABS resin) is preferably used because it has high moldability and makes it easy to obtain the desired pen tip performance.

[0069] Specific examples of the configuration of a ballpoint pen containing an ink composition according to an embodiment of the present invention include: (1) a ballpoint pen having an ink reservoir filled with ink inside the barrel, to which a ballpoint pen tip is connected directly or via a connecting member, and to which an ink backflow prevention body is filled at the end face of the ink; (2) a ballpoint pen in which ink is directly filled inside the barrel, and a mechanism is provided to supply ink to the pen tip by interposing an ink flow control body consisting of a comb-shaped ink flow control body or an ink guide core made of a fiber bundle or the like as an ink flow control body; and (3) a ballpoint pen in which ink is directly filled inside the barrel, and a mechanism is provided to supply ink to the pen tip via the above-mentioned pen core.

[0070] (Marking pen) When writing instrument ink is used in a marking pen, the structure and shape of the marking pen itself are not particularly limited. For example, it can be used by filling a marking pen refill or marking pen, which is equipped with a marking pen tip and an ink filling mechanism.

[0071] Examples of marking pen tips include conventional porous materials with interconnected pores selected from a range of approximately 30-70% porosity, such as resin processed fiber bodies, heat-meltable fiber fused bodies, and felt bodies, or extruded synthetic resin bodies having multiple ink outlets extending in the axial direction. One end is processed into a shape such as a bullet shape, rectangle, or chisel shape according to the purpose for practical use.

[0072] An example of an ink filling mechanism is an ink-absorbing body that can be filled with ink. The ink-absorbing material is a fiber bundle formed by gathering crimped fibers in the longitudinal direction, and is constructed by embedding it in a plastic cylinder or a covering such as a film, and adjusting the porosity to be in the range of approximately 40-90%. A marking pen can be formed by housing an ink-impregnated ink-absorbing material inside the barrel, and connecting a marking pen tip to the barrel, either directly or via a connecting member, so as to connect to the ink-absorbing material.

[0073] Furthermore, a marking pen refill (hereinafter sometimes referred to as "refill") can be formed by housing an ink-impregnated ink reservoir in an ink container, and connecting a marking pen tip to the ink reservoir, either directly or via a connecting member. A marking pen can be formed by housing this refill in a barrel.

[0074] A marking pen comprising a marking pen tip and an ink filling mechanism may further include an ink supply mechanism for supplying ink to be filled into the ink filling mechanism to the pen tip.

[0075] The ink supply mechanism is not particularly limited; for example, in addition to the ink supply mechanism provided in the ballpoint pen described above, (4) a mechanism that provides an ink flow rate regulator by a valve mechanism and supplies ink to the pen tip by opening the valve can be used. The valve mechanism can use a conventional pumping type that opens when pressed by the tip, and it is preferable that the spring pressure is set to allow it to be opened by the pressure of a pen.

[0076] If the marking pen is equipped with an ink supply mechanism, in addition to the ink absorbent described above, an ink container that can be directly filled with ink can be used as the ink filling mechanism. Alternatively, the barrel itself may be used as the ink filling mechanism, and the ink may be filled directly into it.

[0077] Specific examples of marking pen configurations for containing an ink composition according to embodiments of the present invention include: (1) a marking pen in which an ink-absorbing body made of a fiber bundle impregnated with ink is contained within a barrel, and a marking pen tip made of a fiber processed body or resin molded body with capillary gaps formed therein is connected to the barrel directly or via a connecting member so as to connect the ink-absorbing body and the tip; (2) a marking pen in which ink is directly filled into the barrel, and a mechanism is provided to supply ink to the pen tip by interposing an ink-guiding core made of a comb-groove-shaped ink flow regulator or a fiber bundle as an ink flow regulator; (3) a marking pen in which ink is directly filled into the barrel, and a mechanism is provided to supply ink to the pen tip via the pen core described above; and (4) a marking pen in which a tip and an ink-containing body are provided via a valve mechanism that opens when the tip is pressed, and ink is directly filled into the ink-containing body.

[0078] If the ballpoint pen or marking pen according to the present invention is directly filled with ink, an agitator, such as an agitating ball, can be incorporated into the ink container or barrel in which the ink is filled, in order to facilitate the redispersion of the microcapsule pigment.

[0079] The writing instrument according to the present invention, such as a ballpoint pen or marking pen, can also be in the form of a detachable ink cartridge. In this case, after the ink contained in the ink cartridge of the writing instrument is used up, the writing instrument can be used again by replacing it with a new ink cartridge. Ink cartridges can be either those that connect to the writing instrument body and also serve as the barrel of the writing instrument, or those that cover and protect the barrel (rear barrel) after being connected to the writing instrument body. In the latter case, the ink cartridge may be used alone, or the writing instrument may have the writing instrument body and ink cartridge already connected before use, or the ink cartridge may be housed in the barrel in an unconnected state so that the user can connect it when using the writing instrument to begin use.

[0080] The writing instrument according to the present invention, such as a ballpoint pen or marking pen, is provided with a cap that covers the pen tip (writing tip), thereby preventing contamination or damage to the writing tip. Furthermore, writing instruments such as ballpoint pens or marking pens in which a refill is housed inside the barrel can be made into retractable writing instruments by providing a retractable mechanism inside the barrel that allows the writing tip to extend and retract from the barrel, thereby preventing contamination or damage to the writing tip.

[0081] Any retractable writing instrument can be used if its tip is housed within the barrel and the tip protrudes from the barrel when the retraction mechanism is activated. Examples of retractable / retractable mechanisms include: (1) a side-slide type retractable / retractable mechanism in which an operating part (clip) that can move in the front-to-back direction is provided protruding radially outward from the rear side wall of the barrel, and the writing tip is extended and retracted from the front end opening of the barrel by sliding the operating part forward; (2) a rear-end knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part provided at the rear end of the barrel forward; (3) a side-knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part that protrudes from the outer surface of the side wall of the barrel radially inward; and (4) a rotary (twist) type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by rotating an operating part at the rear of the barrel.

[0082] The form of the ballpoint pen or marking pen is not limited to the configuration described above, and may be a multi-function writing instrument (double-ended or retractable tip, etc.). Examples of multi-function writing instruments include (1) a writing instrument equipped with tips of different shapes, (2) a writing instrument equipped with tips that dispense ink of different shades or hues, and (3) a writing instrument equipped with tips of different shapes, in addition to the fact that the ink dispensed from each tip is of different shades or hues.

[0083] [External force application means] The writing instrument may be equipped with an external force application means, and a writing instrument that allows for easy writing and erasing of writing marks can be obtained. As the external force application means provided in the writing instrument, a friction member made of the above-mentioned elastic material is preferred because it can constitute a writing instrument component and is easy to attach to the writing instrument. Alternatively, a writing instrument and an external force application means of any shape, separate from the writing instrument, may be combined to form a writing instrument set. As the external force application means separate from the writing instrument, a friction body made of the above-mentioned elastic material is preferred because it is easy to process into any shape and offers excellent portability.

[0084] In the case of writing instruments equipped with a cap, the location where the friction element is provided is not particularly limited. For example, the cap itself may be formed from a friction element, the barrel itself may be formed from a friction element, or if a clip is provided, the clip itself may be formed from a friction element, or a friction element may be provided at the tip (top) of the cap or the rear end of the barrel (the part without the writing tip).

[0085] In the case of writing instruments equipped with a retractable mechanism, the location where the friction member is provided is not particularly limited. For example, the barrel itself may be formed from the friction member, or if a clip is also provided, the clip itself may be formed from the friction member, or the friction member may be provided near the front end of the barrel, at the rear end of the barrel (the part without the writing tip), or at the knock mechanism.

[0086] The writing instrument according to the present invention can be used, for example, as follows. The writing instrument according to the present invention forms an arbitrary image (handwriting) on ​​a writing surface (e.g., black paper). An external force application means (e.g., a friction member or friction body) is pressed against the area where the image has been formed and rubbed. When the microcapsule pigment in the rubbed area is destroyed, the image in the area where the external force application means was applied becomes invisible and the image is erased. The same writing instrument can be used again to form an image in the area where the image has been erased and erased in the same way. Therefore, the formation and erasure of images can be repeatedly performed on the same writing surface.

[0087] The ink composition according to the present invention can be used for purposes other than writing instruments. For example, it can be used as a printing ink for screen printing, offset printing, process printing, gravure printing, coater, pad printing, etc.; a paint for brush coating, spray coating, electrostatic coating, electrodeposition coating, pour coating, roller coating, dipping coating, etc.; an inkjet ink; an ultraviolet-curing ink; an ink for applicators; an ink for stamps; a paint; a cosmetic; and a coloring liquid for textiles. [Examples]

[0088] Examples are shown below. Unless otherwise specified, "parts" in the examples refer to "parts by mass." The melting point of the inclusions (crystalline compound) described later was measured using a melting point measuring device [Mettler Toledo K.K., product name: FP900 Thermo System (a device consisting of an FP90 Central Processor and an FP81HT MBC Cell)] in a temperature range of -20°C to 80°C at a heating rate of 1°C / min. The crystalline compound was prepared as a sample for measurement by filling a transparent glass capillary with an inner diameter of 1 mm and a length of 78 mm to a height of 10 mm from the bottom of the capillary.

[0089] Example 1 [Preparation of microencapsulated pigments] Fifty parts of stearyl caprate (melting point: 39°C) as the encapsulant (crystalline compound), 12.5 parts of aromatic isocyanate prepolymer as the wall-forming material, and 40 parts of a co-solvent were added to a mixed solution. The mixture was then emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution, and stirring was continued while heating. Then, 2.5 parts of a water-soluble aliphatic modified amine were added, and stirring was continued to prepare a microcapsule dispersion. Microcapsule pigments were obtained from the above microcapsule dispersion by centrifugation. The average particle size of the microcapsule pigment was 2.3 μm. The average particle size was calculated as described above.

[0090] [Manufacturing of writing instruments (ballpoint pens)] A water-based ink composition for writing instruments was prepared by mixing 25 parts of the microcapsule pigment from Example 1 (pre-cooled to -20°C or below) as a coloring agent, 0.3 parts of a shear viscosity reducing agent (xanthan gum), 10 parts of urea, 10 parts of glycerin, 0.5 parts of a nonionic penetrating agent [Sunopco Co., Ltd., product name: Nopco SW-WET-366], 0.1 parts of a modified silicone defoaming agent [Sunopco Co., Ltd., product name: Nopco 8034], 0.5 parts of a phosphate ester surfactant [Daiichi Kogyo Seiyaku Co., Ltd., product name: Prisurf AL], 0.5 parts of a pH adjuster (triethanolamine), 0.2 parts of an antifungal agent [Arcsaada Japan Co., Ltd., product name: Proxel XL-2(S)], and 52.9 parts of water. The above ink composition was suction-filled into an ink reservoir made of polypropylene pipe, and then connected to a ballpoint pen tip holding a 0.5 mm diameter carbide ball at its tip via a resin holder. Next, a viscoelastic ink backflow prevention body (liquid stopper) mainly composed of polybutene was filled into the rear end of the ink reservoir to create a ballpoint pen refill. The above refill was assembled into the barrel to obtain a ballpoint pen (retractable ballpoint pen). The ballpoint pen described above has a structure in which the tip of the ballpoint pen refill is housed inside the barrel with the tip exposed to the outside air, and the tip protrudes from the opening at the front of the barrel by the operation of a clip-shaped retraction mechanism (slide mechanism) provided on the rear side wall of the barrel. Furthermore, a friction member made of SEBS resin is attached to the rear end of the barrel as a means of applying external force.

[0091] Example 2 [Preparation of microencapsulated pigments] Microcapsule pigments were obtained by the same method as in Example 1, except that the encapsulated substance (crystalline compound) was changed to 4-benzyloxyphenylethyl caprate (melting point: 64°C). The average particle size of the microcapsule pigments described above was 2.0 μm. The average particle size was calculated as described above.

[0092] [Manufacturing of writing instruments (ballpoint pens)] A water-based ink composition for writing instruments was prepared by mixing 25 parts of the microcapsule pigment from Example 2 (pre-cooled to -20°C or below) as a coloring agent, 0.3 parts of a shear viscosity reducing agent (xanthan gum), 10 parts of urea, 10 parts of glycerin, 0.5 parts of a nonionic penetrating agent [Sunopco Co., Ltd., product name: Nopco SW-WET-366], 0.1 parts of a modified silicone defoaming agent [Sunopco Co., Ltd., product name: Nopco 8034], 0.5 parts of a phosphate ester surfactant [Daiichi Kogyo Seiyaku Co., Ltd., product name: Prisurf AL], 0.5 parts of a pH adjuster (triethanolamine), 0.2 parts of an antifungal agent [Arcsaada Japan Co., Ltd., product name: Proxel XL-2(S)], and 52.9 parts of water. Using the above ink composition, a ballpoint pen (retractable ballpoint pen) was prepared in the same manner as in Example 1.

[0093] Example 3 [Manufacturing of writing instruments (marking pens)] As a coloring agent, 23 parts of the microcapsule pigment from Example 2 (pre-cooled to -20°C or below) were used, along with a polymer flocculant (hydroxyethylcellulose) [manufactured by Dow Chemical Japan Ltd., product name: CELLOSIZE]. A water-based ink composition for writing instruments was prepared by mixing 0.4 parts of WP-09L, 0.4 parts of an acrylic polymer dispersant [manufactured by Lubrizol Japan Co., Ltd., product name: Solspers 43000], 0.2 parts of a preservative (2-pyridinethiol 1-oxide sodium) [manufactured by Arcsada Japan Co., Ltd., product name: sodium omazine], 0.2 parts of a preservative (3-iodo-2-propynyl N-butylcarbamate) [manufactured by Arcsada Japan Co., Ltd., product name: Glycasil 2000], 30 parts of glycerin, 0.01 parts of an antifoaming agent, 0.03 parts of a pH adjuster (10% diluted phosphoric acid solution), and 45.76 parts of water in an aqueous vehicle. The above ink composition was impregnated into an ink-absorbing body made of polyester sliver coated with a synthetic resin film, and housed in a barrel made of polypropylene resin. A resin-processed pen body (bullet-shaped) made of polyester fiber was attached to the tip of the barrel via a resin holder, and a cap was attached to create a marking pen (capped marking pen). A friction member made of SEBS resin was attached to the tip (top) of the cap as a means of applying external force.

[0094] Example 4 [Preparation of microencapsulated pigments] Microcapsule pigments were obtained by the same method as in Example 1, except that the encapsulated substance (crystalline compound) was changed to cetyl 2-ethylhexanoate (melting point: -5°C). The average particle size of the microcapsule pigments described above was 2.1 μm. The average particle size was calculated as described above.

[0095] [Manufacturing of writing instruments (ballpoint pens)] A water-based ink composition for writing instruments was prepared by mixing 25 parts of the microcapsule pigment from Example 4 as a coloring agent, 0.3 parts of a shear viscosity reducing agent (xanthan gum), 10 parts of urea, 10 parts of glycerin, 0.5 parts of a nonionic penetrating agent [Sunopco Co., Ltd., product name: Nopco SW-WET-366], 0.1 parts of a modified silicone defoaming agent [Sunopco Co., Ltd., product name: Nopco 8034], 0.5 parts of a phosphate ester surfactant [Daiichi Kogyo Seiyaku Co., Ltd., product name: Prisurf AL], 0.5 parts of a pH adjuster (triethanolamine), 0.2 parts of an antifungal agent [Arcsaada Japan Co., Ltd., product name: Proxel XL-2(S)], and 52.9 parts of water. Using the above ink composition, a ballpoint pen (retractable ballpoint pen) was prepared in the same manner as in Example 1.

[0096] Comparative Example 1 [Preparation of microencapsulated pigments] Fifty parts of cetyl 2-ethylhexanoate (melting point: -5°C) as the encapsulant (crystalline compound), 25 parts of aromatic isocyanate prepolymer as the wall-forming material, and 40 parts of a co-solvent were added to a mixed solution. The mixture was then emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution, and stirring was continued while heating. Then, 2.5 parts of a water-soluble aliphatic modified amine were added, and stirring was continued to prepare a microcapsule dispersion. Microcapsule pigments were obtained from the above microcapsule dispersion by centrifugation. The average particle size of the microcapsule pigment was 3.0 μm. The average particle size was calculated as described above.

[0097] [Manufacturing of writing instruments (ballpoint pens)] A water-based ink composition for writing instruments was prepared by mixing 25 parts of the microcapsule pigment from Comparative Example 1 as a coloring agent, 0.3 parts of a shear viscosity reducing agent (xanthan gum), 10 parts of urea, 10 parts of glycerin, 0.5 parts of a nonionic penetrating agent [Sunopco Co., Ltd., product name: Nopco SW-WET-366], 0.1 parts of a modified silicone-based defoaming agent [Sunopco Co., Ltd., product name: Nopco 8034], 0.5 parts of a phosphate ester-based surfactant [Daiichi Kogyo Seiyaku Co., Ltd., product name: Prisurf AL], 0.5 parts of a pH adjuster (triethanolamine), 0.2 parts of an antifungal agent [Arcsaada Japan Co., Ltd., product name: Proxel XL-2(S)], and 52.9 parts of water. Using the above ink composition, a ballpoint pen (retractable ballpoint pen) was prepared in the same manner as in Example 1.

[0098] [Preparation of test samples] Using the ballpoint pens and marking pens prepared in Examples 1-4 and Comparative Example 1, under room temperature (20°C), A4 size black paper (portrait orientation) [(Nagatoya Shoten Co., Ltd., product name: Color Paper A4 Medium Thickness (thickness: 0.09 mm, density: 80 g / m²)] was used. 2 Twelve elliptical circles (approximately 15mm in major axis and 8mm in minor axis) were handwritten in a spiral pattern, one line at a time, perpendicular to the longitudinal direction of the ) and in the horizontal direction, with the circles touching each other.

[0099] [Opacity (handwriting density) evaluation] The obtained handwriting samples were visually inspected, and their opacity (handwriting density) was evaluated according to the following criteria. The evaluation results are shown in Table 1 below. Evaluations "A" and "B" were considered acceptable. All handwriting samples were free from smudging or breaks and were of good quality. A: The handwriting was clearly white, and the black of the underlying paper was not visible through the handwriting, indicating sufficient opacity. B: The handwriting was a light white, and in some places the black of the underlying paper was visible through the handwriting, but the opacity was at a level that did not pose any practical problems. C: The handwriting was noticeably faint white, and the black of the underlying paper was clearly visible through the handwriting, indicating insufficient opacity.

[0100] [Confirming the erase function] The results were checked to see if the handwriting could be erased when rubbed with an external force application means (friction member) provided on the writing instrument. The evaluation results are shown in Table 1 below. An evaluation of "A" was considered a pass. A: The microcapsules in the rubbed area were destroyed, and the handwriting on the paper was erased. B: The microcapsules in the rubbed area were not destroyed, the handwriting on the paper was not erased, and it remained clearly visible.

[0101] [Table 1]

[0102] Application Example 1 [Fabrication of laminates] Forty parts of the microcapsule pigment from Example 2 (pre-cooled to -20°C or below), 52 parts of ethylene-vinyl acetate copolymer resin emulsion, 5 parts of a thickener, and 3 parts of a leveling agent were mixed to prepare a screen printing ink composition. Using the above ink composition, black paper [(manufactured by Nagatoya Shoten Co., Ltd., product name: Color Paper A4 medium thickness (thickness: 0.09 mm, density: 80 g / m²)] was used. 2 A solid pattern was screen printed onto the black paper, dried and hardened to create a colored layer on the black paper, and a laminate was obtained.

[0103] This laminate exhibited a clearly white colored layer with good opacity, preventing the black color of the underlying paper from being visible through the colored layer. When a friction body made of dome-shaped SEBS resin was used to rub the colored layer of this laminate in a way that formed the image of the character "あ", the microcapsules in the rubbed area were destroyed, and a black image (the cut-out character "あ") appeared on a white background. This image was formed irreversibly, and the rubbed area was not visible on the paper, resulting in excellent contrast between the background and the character, and the image was clearly visible.

[0104] Application Example 2 [Making a correction tool] Twenty parts of the microcapsule pigment from Example 1 (pre-cooled to below -20°C) were mixed with a polymer flocculant (hydroxyethylcellulose) [manufactured by Dow Chemical Japan Ltd., product name: CELLOSIZE]. A water-based ink composition for correction tools was prepared by mixing 0.4 parts of WP-09L, 0.4 parts of an acrylic polymer dispersant [manufactured by Lubrizol Japan Co., Ltd., product name: Solspers 43000], 0.2 parts of a preservative (2-pyridinethiol 1-oxide sodium) [manufactured by Arcsada Japan Co., Ltd., product name: sodium omazine], 0.2 parts of a preservative (3-iodo-2-propynyl N-butylcarbamate) [manufactured by Arcsada Japan Co., Ltd., product name: Glycasil 2000], 30 parts of glycerin, 0.01 parts of an antifoaming agent, 0.03 parts of a pH adjuster (10% diluted phosphoric acid solution), and 45.76 parts of water in an aqueous vehicle. The above ink composition was impregnated into an ink-absorbing body made of polyester sliver coated with a synthetic resin film, and housed in a barrel made of polypropylene resin. A resin-processed pen body (chisel type) made of polyester fiber was assembled to the tip of the barrel via a resin holder, and a cap was attached to create a correction tool (cap-type marking pen correction tool). A friction member made of SEBS resin was attached to the rear end of the barrel as a means of applying external force.

[0105] When writing on white paper with a regular black ballpoint pen, if a writing error occurred, the error could be concealed by applying the ink composition using the correction tool described above. The correct writing could then be done over the concealed area using a black ballpoint pen. Furthermore, if the ink composition was unintentionally applied to an area that did not need correction, the unwanted concealed portion could be erased by rubbing that area with the friction material, allowing the written character to reappear in that area.

[0106] Application Example 3 [Making a writing instrument (memorization pen)] Fifteen parts of the microcapsule pigment from Example 2 (pre-cooled to below -20°C) were mixed in an aqueous vehicle consisting of 0.4 parts of a polymer flocculant (hydroxyethylcellulose) [manufactured by Dow Chemical Japan Ltd., product name: CELLOSIZE WP-09L], 5 parts of glycerin, 0.7 parts of a preservative [manufactured by Arcsarda Japan Co., Ltd., product name: Proxel XL-2(S)], 0.1 parts of a silicone-based defoamer [manufactured by Sunopco Co., Ltd., product name: SN Deformer 381], and 78.8 parts of water to prepare an aqueous ink composition for writing instruments. The above ink composition was impregnated into an ink-absorbing body made of polyester sliver coated with a synthetic resin film, and housed in a barrel made of polypropylene resin. A resin-processed pen body (chisel type) made of polyester fiber was assembled to the tip of the barrel via a resin holder, and a cap was attached to create a writing instrument (capped memorization pen). A friction member made of silicone resin was attached to the rear end of the barrel as a means of applying external force.

[0107] When an ink composition was applied to the parts of the black text printed on white paper that needed to be memorized using a writing instrument (memorization pen), the black text in those areas became invisible and could not be seen, allowing for memorization. Furthermore, when the hidden text needed to be reviewed again, or when memorization was completed and the hidden parts no longer needed to be memorized, the hidden areas could be erased by rubbing them with a friction material, and the printed text in those areas could be made to reappear.

Claims

1. A water-based ink composition for writing instruments comprising microcapsule pigments that are destroyed by the application of an external force, and water, wherein the microcapsule pigments contain at least one compound selected from the group consisting of crystalline esters, ethers, and ketones, having a melting point in the range of -40 to 95°C.

2. The ink composition according to claim 1, wherein the melting point of the compound is in the range of 35°C to 90°C.

3. The ink composition according to claim 1, wherein the external force applying means is a friction member or friction body.

4. A writing instrument comprising an ink composition according to any one of claims 1 to 3.

5. The writing instrument according to claim 4, further comprising a friction member as the means for applying the external force.

6. A writing instrument set comprising the writing instrument described in claim 4 and the friction body as the means for applying external force.

7. A method for using a writing instrument, characterized by using a writing instrument containing an aqueous ink composition for writing instruments, which comprises a microcapsule pigment that is destroyed by the application of an external force means and water, wherein the microcapsule pigment contains at least one compound selected from the group consisting of crystalline esters, ethers, and ketones having a melting point in the range of -40 to 95°C, to form an image on a writing surface, and then applying the external force means to the image to destroy the microcapsule pigment and erase the image.

8. The method of using the writing instrument according to claim 7, wherein the melting point of the compound is in the range of 35°C to 90°C.

9. The method of using a writing instrument according to claim 7 or 8, wherein the external force applying means is a friction member or friction body.

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