Aqueous ink composition for pills, and pills containing said aqueous ink composition for pills

Abstract

An aqueous ink composition for a pen includes water, a colorant, and sulfated cellulose fibers in which at least a portion of hydroxyl groups of the cellulose fibers are sulfated.

Description

Technical Field

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

[0002] In the past, inks with water as the main solvent (aqueous inks) were widely used because of their low odor and high safety. Generally, the dispersion stability of colorants such as pigments and resin particles in water is unstable. If the colorants are not dispersed uniformly in advance to be in a stable state, coagulation and / or sedimentation will occur, and the concentration of the handwriting formed by the writing instrument containing the ink will decrease, or the ink discharge from the pen tip will decrease, resulting in poor writing such as flying lines and flying whites, etc., and it is sometimes difficult to obtain sufficient performance for aqueous inks used as writing instruments. Therefore, the following ink composition is disclosed: various dispersants and / or additives are used to improve the dispersion stability of pigments or resin particles in aqueous inks (for example, refer to patent documents 1 to 3).

[0003] Patent Document 1 discloses an aqueous ink composition containing water, a pigment, and an alkali salt of a carboxyl group-containing compound as a dispersant.

[0004] Patent Document 2 discloses an aqueous ink containing water, a pigment, xanthan gum, and non-crosslinked polyacrylic acid having a specific molecular weight or a salt thereof.

[0005] Patent Document 3 discloses an aqueous ink composition including a pigment, an aqueous medium, and a copolymer of an N-vinylpyrrolidone derivative and an acrylic acid derivative or a methacrylic acid derivative as a dispersant.

[0006] In addition, when the pen is stored with the pen tip facing downward, so-called dripping, in which ink drops accumulate at the tip of the pen, is likely to occur. With regard to the dripping, attempts have been made to suppress it by increasing the viscosity of the ink when it is left standing using a shear-thinning agent or by using various additives (for example, see Patent Documents 4 to 5).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2004-018675

[0010] Patent Document 2: Japanese Patent Application Publication No. 2004-059877

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 09-059554

[0012] Patent Document 4: Japanese Patent Application Publication No. 2006-77074

[0013] Patent Document 5: Japanese Patent Application Publication No. 2013-103986 Summary of the invention

[0014] Problems to be solved by the invention

[0015] The aqueous ink (aqueous ink composition) disclosed in Patent Documents 1 to 3 can stably disperse the colorant in the ink by using a dispersant or a resin. However, it is known that in the prior art disclosed in Patent Documents 1 to 3, the dispersion stability of the colorant in the ink is still insufficient, and it is difficult to suppress the aggregation and / or sedimentation of the pigment for a long time, especially when the particle size of the pigment is large and / or the specific gravity is high, which sometimes causes a decrease in the handwriting density and / or poor writing.

[0016] In addition, when using the shear-thinning imparting agent to make the ink high viscosity when standing, although the ink can be suppressed to a certain extent from the dripping of the nib, it is possible that the drying performance deteriorates and / or the handwriting is prone to produce the deterioration of writing performance such as flying white along with the high viscosity. In order to eliminate the described undesirable situation, in patent documentation 4, xanthan gum or succinoglycan is used as the shear-thinning imparting agent, and polyvinylpyrrolidone is used in combination with a specific ratio. By the described formation, although the dripping and the drying of the nib when standing can be effectively suppressed, when writing, paper fibers etc. are sandwiched between the ball and the small mouth, or are placed in the state of pressing the ball, or the nib front end is damaged or deformed because of falling, etc., and when the ink flow path is unexpectedly expanded, when keeping at high temperature or high humidity, the dripping of the ink sometimes occurs or further deteriorates and drips. And, when writing out due to the rotation of the ball and the low shear load, flying white is easily produced, and the sense of writing also becomes heavy.

[0017] In this regard, Patent Document 5 discloses the following technology: instead of relying on viscosity adjustment based on shear-thinning agents, crystalline cellulose and resin particles are added together, whereby the resin particles inhibit the sedimentation of the crystalline cellulose in the ink over time and increase the anti-DC effect, thereby achieving a high degree of both anti-DC effect and stability over time without reducing writing performance.

[0018] However, it is known that even if the technology of Patent Document 5 is used, sufficient effects cannot be obtained for the above-mentioned unexpected expansion of the ink flow path or storage under high temperature and high humidity, and ink dripping may occur. In addition, it is also known that crystalline cellulose is a large particle of 10 μm or more obtained by using pulp as a raw material, extracting cellulose crystal regions by hydrolysis and purifying, and therefore, due to the centrifugal load during the manufacture of the writing instrument and / or the long-term lapse of time in the same posture, sometimes sedimentation occurs on the pen tip side, hindering the flow of ink during writing.

[0019] The present disclosure provides an aqueous ink composition for writing instruments and a writing instrument containing the aqueous ink composition for writing instruments, wherein the aqueous ink composition for writing instruments can solve at least one of the following technical problems 1 and 2.

[0020] Technical problem 1: The colorant is not prone to agglomeration and / or sedimentation over time, and can form good handwriting.

[0021] Technical Problem 2: When the pen is stored for a long time with the nib facing downward, no dripping will occur and good handwriting without flying white can be formed.

[0022] Solutions for solving problems

[0023] A first aspect of the present invention is a water-based ink composition for writing instruments, comprising water, a colorant, and sulfated cellulose fibers in which at least a part of hydroxyl groups of the cellulose fibers are sulfated.

[0024] Aspect 2 of the present invention is the aqueous ink composition for writing instruments according to aspect 1, wherein the sulfated cellulose fibers have a cellulose I-type crystal structure, and at least part of the hydrogen atoms of the hydroxyl groups of the cellulose fibers are substituted with sulfonic groups represented by the following formula (1).

[0025] (-SO3 － ) r ·Z r+ ……(1)

[0026] [where r is a natural number from 1 to 3. When r = 1, Z r+ is at least one selected from the group consisting of hydrogen ions, alkali metal cations, ammonium ions, aliphatic ammonium ions, and aromatic ammonium ions. When r=2 or 3, Z r+ At least one selected from the group consisting of alkaline earth metal cations and polyvalent metal cations.]

[0027] A third aspect of the present invention is the aqueous ink composition for writing instruments according to the first or second aspect, wherein the average fiber width of the sulfated cellulose fibers is 0.5 to 500 nm.

[0028] A fourth aspect of the present invention is the aqueous ink composition for writing instruments according to the third aspect, wherein the average fiber width of the sulfated cellulose fibers is 30 nm or less.

[0029] A fifth aspect of the present invention is the aqueous ink composition for writing instruments according to any one of aspects 1 to 4, wherein the amount of sulfur introduced into the sulfated cellulose fibers is higher than 0.42 mmol / g.

[0030] A sixth aspect of the present invention is the aqueous ink composition for writing instruments according to any one of the first to fifth aspects, wherein the degree of polymerization of the sulfated cellulose fibers is 30 or more.

[0031] Aspect 7 of the present invention is the aqueous ink composition for writing instruments according to any one of aspects 1 to 6, wherein the haze value of the dispersion obtained by dispersing the sulfated cellulose fibers in a water-soluble solvent so as to have a solid content concentration of 0.5% by mass is 20% or less.

[0032] Aspect 8 of the present invention is the aqueous ink composition for writing instruments according to any one of aspects 1 to 7, wherein the sulfated cellulose fibers are blended in an amount within a range of 0.01 to 3% by mass in the total amount of the ink composition.

[0033] A ninth aspect of the present invention is the aqueous ink composition for writing instruments according to any one of the first to eighth aspects, further comprising a shear-thinning property-imparting agent.

[0034] Aspect 10 of the present invention is the aqueous ink composition for writing instruments according to aspect 9, wherein the shear-thinning agent is any one or more selected from the group consisting of water-soluble polysaccharides, polymers having a molecular weight of 100,000 to 150,000 and containing an alkyl ester of methacrylic acid as a main component, poly-N-vinylcarboxylic acid amide crosslinked products, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali thickening type acrylic resins, crosslinked acrylic polymers, inorganic fine particles, nonionic surfactants having an HLB value of 8 to 12, and metal salts or amine salts of dialkyl sulfosuccinic acids.

[0035] Aspect 11 of the present invention is the aqueous ink composition for writing instruments according to aspect 9 or 10, wherein the shear-thinning agent is blended in an amount within a range of 0.05 to 1% by mass based on the total amount of the ink composition.

[0036] A twelfth aspect of the present invention is the aqueous ink composition for writing instruments according to any one of aspects 1 to 11, wherein the colorant is dispersed in water.

[0037] A thirteenth aspect of the present invention is the aqueous ink composition for writing instruments according to any one of the first to twelfth aspects, wherein the colorant includes at least one selected from the group consisting of pigments and resin particles.

[0038] A fourteenth aspect of the present invention is the aqueous ink composition for writing instruments according to any one of the first to thirteenth aspects, wherein the colorant has an average particle size of 0.01 to 25 μm.

[0039] A fifteenth aspect of the present invention is the aqueous ink composition for writing instruments according to any one of the first to fourteenth aspects, comprising a colorant having a specific gravity greater than 1.

[0040] A sixteenth aspect of the present invention is a writing instrument containing the aqueous ink composition for writing instruments according to any one of the first to fifteenth aspects.

[0041] Effects of the Invention

[0042] According to an embodiment of the present invention, a water-based ink composition for writing instruments and a writing instrument containing the water-based ink composition for writing instruments can be provided, wherein the colorant of the water-based ink composition for writing instruments is not easy to coagulate and / or settle over time, and good handwriting can be formed; and / or when the writing instrument is stored for a long time in a state where the nib of the writing instrument is facing downward, no dripping occurs, and good handwriting without flying white and the like can be formed. DETAILED DESCRIPTION

[0043] The aqueous ink composition for writing instruments (hereinafter sometimes referred to as "ink composition" or "ink") according to an embodiment of the present invention contains water, a colorant, and sulfated cellulose fibers. Hereinafter, each component constituting the ink composition according to an embodiment of the present invention will be described.

[0044] The ink composition according to the embodiment of the present invention contains water.

[0045] The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water.

[0046] The content of water relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 35 to 95 mass %, and more preferably in the range of 40 to 90 mass %.

[0047] The ink composition according to the embodiment of the present invention contains a colorant.

[0048] As the colorant, all dyes, pigments and resin particles that can be dissolved or dispersed in an aqueous medium can be used. That is, the colorant can include any one or more selected from the group consisting of a dye, a pigment and a resin particle. For example, the colorant can include any one or more selected from the group consisting of a pigment and a resin particle, or can be composed of any one or more selected from the group consisting of a pigment and a resin particle. In addition, the colorant can include a dye, or can be composed of a dye.

[0049] As the dye, acid dyes, basic dyes, direct dyes and the like can be used.

[0050] As acid dyes, naphthol green B (CI10020), naphthol yellow S (CI10316), acid yellow 9 (CI13015), m-aniline yellow (CI13065), orange I (CI14600), ponceau SX (CI14700), orange II (CI15510), sunset yellow FCF (CI15985), new carmine (CI16255), azo fuchsine (CI16256), and chlorinated carmine (CI16257). Acidmagenta)(CI17200), Acid Azo Red 3G(CI18050), Acid Yellow 3G(CI18820), Tartrazine(CI19140), Resorcinol Brown(CI20170), Acid Blue 29(CI20460), Naphthol Blue Black(CI20470), Acid Orange 56(CI22895), Acid Yellow 42(CI22910), Gini Green B(CI42085), Fast Green FCF(CI42053), Brilliant Blue FCF(CI42090), Acid Violet 6B (CI42640), Acid Blue 1 (CI42045), Brilliant Blue G (CI42655), Brilliant Blue P-1 (CI42735), Aqua Cyan (CI42755), Acid Green B (CI44025), Acid Red (CI45100), Violet R (CI45190), Fluorescein Sodium (CI45350), Eosin (CI45380), Fluorescent Pink B (CI45410), Erythrosine (CI45430), Aniline Black (CI50420), Solvent Green (pyranine conc) (CI59040), Alizarin Cyanine Violet (CI60730), Alizarin Cyanine Green F (CI61570), Indigo Carmine (CI73015), etc.

[0051] As basic dyes, the following can be used: basic orange (CI11270), methyl violet FN (CI42535), crystal violet (CI42555), malachite green (CI42000), Victoria blue FB (CI44045), rhodamine B (CI45170), acridine orange NS (CI46005), methylene blue B (CI52015), etc.

[0052] As direct dyes, Congo Red (CI22120), Direct Lake Blue 5B (CI24400), Purple BB (CI27905), Direct Deep Black EX (CI30235), Kayalus Black G conc (CI35225), Direct Fast Black G (CI35255), Phthalocyanine Blue (CI74180), etc. can be used.

[0053] Examples of the pigment include inorganic pigments, organic pigments, bright pigments, fluorescent pigments, light-storing pigments, etc. In addition, a water-dispersible pigment obtained by finely and stably dispersing the pigment in an aqueous medium using a surfactant and / or a resin may be used.

[0054] Furthermore, a pigment dispersant may be used as required. Examples of the pigment dispersant include anionic and nonionic surfactants, anionic polymers such as polyacrylic acid and styrene-acrylic acid, and nonionic polymers such as PVP and PVA.

[0055] The pigments used in the embodiments of the present invention also include: microcapsule pigments formed by encapsulating dyes such as acid dyes, basic dyes, direct dyes, oil-soluble dyes, disperse dyes, or the above-mentioned pigments in microcapsules. The dyes or pigments are isolated and protected from the external environment by being encapsulated in microcapsules, which can improve the water resistance and light resistance of the inclusions. It should be noted that the aqueous ink composition for writing instruments containing microcapsule pigments containing dyes is included in the scheme of "aqueous ink composition for writing instruments containing pigments", and is also included in the scheme of "aqueous ink composition for writing instruments containing dyes".

[0056] The microcapsule pigment encapsulating a dye or a pigment can be formed by encapsulating a coloring body obtained by dissolving or dispersing the dye or the pigment in an oil medium in microcapsules.

[0057] The pigments used in the embodiments of the present invention also include: microcapsule pigments formed by encapsulating functional materials such as thermochromic materials that change color due to temperature changes and photochromic materials that change color due to light irradiation in microcapsules. These color changes can be reversible or irreversible. Considering that the color changes can be repeatedly reflected due to temperature changes or light irradiation, reversible thermochromic materials or reversible photochromic materials are preferred as functional materials.

[0058] As the reversible thermochromic material, there can be cited a reversible thermochromic composition formed of at least (A) an electron-donating color-forming organic compound, (B) an electron-accepting compound, and (C) a reaction medium that determines the temperature at which the color-forming reaction of the components (A) and (B) occurs. By encapsulating the reversible thermochromic composition in microcapsules, a reversible thermochromic microcapsule pigment can be formed.

[0059] As a reversible thermochromic composition, a heat-decolorizable composition having a small hysteresis width (ΔH) characteristic (ΔH=1-7°C) as described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc. can be used. The heat-decolorizable composition means that the color is removed by heating and the color is developed by cooling. The reversible thermochromic composition changes color around a specified temperature (color change point) as a boundary, and is in a decolorized state in a temperature range above the color change point on the high temperature side, and in a color development state in a temperature range below the color change point on the low temperature side. Only a specific one of the two states exists in the normal temperature range, and the other state is maintained during the application of heat or cold heat required to embody the state, but if heat or cold heat is no longer applied, it returns to the state presented in the normal temperature range.

[0060] As the reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition having a large hysteresis width (ΔH=8 to 80° C.) described in Japanese Patent Publication No. 4-17154, Japanese Patent Application Laid-Open No. 7-179777, Japanese Patent Application Laid-Open No. 7-33997, Japanese Patent Application Laid-Open No. 8-39936, Japanese Patent Application Laid-Open No. 2005-1369, etc. can also be used. The heat-decolorizing type means that the color is removed by heating and the color is developed by cooling. The reversible thermochromic composition changes color along a path whose shape is greatly different in the following cases, where the temperature is increased from the lower temperature side of the color change temperature range and conversely decreased from the higher temperature side of the color change temperature range. The color development state in the temperature range below the complete color development temperature t1 or the color removal state in the high temperature range above the complete color removal temperature t4 has color memory in a specific temperature range [the temperature range between the color development start temperature t2 and the color removal start temperature t3 (the actual two-phase maintenance temperature range)].

[0061] It should be noted that, when the above-mentioned reversible thermochromic composition with color memory is applied in the embodiment of the present invention, as a reversible thermochromic composition, specifically, by specifying the complete color development temperature t1 to a temperature that can only be obtained in a freezer, a cold place, etc., and specifying the complete decolorization temperature t4 to a range of temperatures obtained by friction heat generated by a friction body and a temperature obtained by a close-fitting heating body such as a hair dryer, and specifying the ΔH value to 40 to 100°C, the function of maintaining the color presented in normal conditions (daily life temperature range) can be effectively exerted.

[0062] The temperature that can be obtained only in a freezer room, a cold place, etc. is in the range of -50 to 0°C, preferably -40 to -5°C, and more preferably -30 to -10°C.

[0063] The temperature obtained by a close-fitting heating body such as a hair dryer is in the range of 50 to 95°C, preferably 50 to 90°C, and more preferably 60 to 80°C.

[0064] As the reversible thermochromic composition, a heat-discoloring type reversible thermochromic composition using a gallic acid ester described in Japanese Patent Publication No. 51-44706, Japanese Patent Application Laid-Open No. 2003-253149, etc. can be used.

[0065] The heat-developing type is a type that develops color by heating and fades by cooling.

[0066] The reversible thermochromic composition is a phase solvent with the above-mentioned (A) component, (B) component and (C) component as essential components. The ratio of each component is affected by the concentration, color change temperature, color change form and / or the type of each component. The component ratio for obtaining the desired properties is usually in the following range: relative to 1 of (A) component, (B) component is 0.1 to 100, preferably 0.1 to 50, more preferably 0.5 to 20, and (C) component is 1 to 800, preferably 5 to 200, more preferably 5 to 100, and further preferably 10 to 100 (the above ratios are all parts by mass).

[0067] As reversible photochromic materials, there can be listed: previously known photochromic compounds such as spirooxazine derivatives, spiropyran derivatives, and naphthopyran derivatives, which develop color when irradiated with sunlight, ultraviolet light, or blue light with a peak emission wavelength in the range of 400 to 495 nm, and fade when the irradiation is stopped. For example, the compounds described in Japanese Patent Gazette No. 2021-120493 and International Publication No. 2020 / 137469 can be exemplified.

[0068] Furthermore, a photochromic compound having light memory properties (color memory photochromic properties) may also be used. Examples of such photochromic compounds include diarylethene derivatives, and for example, compounds described in Japanese Unexamined Patent Publication No. 2021-120493 may be cited.

[0069] As the reversible photochromic material, a reversible photochromic composition obtained by dissolving the above-mentioned photochromic compound in oligomers such as styrene oligomers, acrylic oligomers, terpene oligomers, terpene phenolic oligomers, etc. can also be used. By encapsulating the reversible photochromic composition in microcapsules, a reversible photochromic microcapsule pigment can be formed.

[0070] By dissolving the photochromic compound in various oligomers, the light resistance can be improved, the color concentration can be increased, and the color change sensitivity can be adjusted.

[0071] The microencapsulation of microcapsule pigments includes conventionally known isocyanate-based interfacial polymerization methods, melamine-formaldehyde-based in-situ polymerization methods, liquid solidification coating methods, phase separation methods from aqueous solutions, phase separation methods from organic solvents, melt dispersion cooling methods, air suspension coating methods, spray drying methods, etc., which are appropriately selected according to the application. As the material of the capsule, for example, epoxy resin, urea resin, urethane resin, isocyanate resin, etc. can be exemplified.

[0072] Furthermore, a secondary resin film may be further provided on the surface of the microcapsule to impart durability or to modify the surface properties for practical use, depending on the purpose.

[0073] The reversible thermochromic microcapsule pigment or reversible photochromic microcapsule pigment preferably has a mass ratio of inner substance to wall film of 7:1 to 1:1. When the mass ratio of inner substance to wall film is within the above range, the decrease in color concentration and vividness during color development can be prevented. More preferably, the mass ratio of inner substance to wall film is 6:1 to 1:1.

[0074] The reversible thermochromic microcapsule pigment or the reversible photochromic microcapsule pigment can also be prepared into a microcapsule pigment that exhibits a color change behavior from colored (1) to colored (2) by adding a non-color-changing colorant such as a common dye or pigment to the microcapsule.

[0075] As resin particles, there can be cited: resin particles containing the above-mentioned dyes, pigments, thermochromic materials and / or photochromic materials. It should be noted that resin particles containing dyes are included in the scheme of "aqueous ink composition for writing instruments containing resin particles" and are also included in the scheme of "aqueous ink composition for writing instruments containing dyes". In addition, resin particles containing pigments are included in the scheme of "aqueous ink composition for writing instruments containing resin particles" and are also included in the scheme of "aqueous ink composition for writing instruments containing pigments".

[0076] Examples of the resin particles containing a dye include colored resin particles in which a dye is uniformly dissolved or dispersed in the resin particles and colored resin particles in which a dye is dyed and attached to the resin particles.

[0077] Examples of the pigment-containing resin particles include: colored resin particles in which the pigment is uniformly dispersed in the resin particles, and colored resin particles in which the surface of the resin particles is coated with the pigment, etc. Here, the pigment may be surface-treated by various conventionally known methods for the purpose of improving the dispersibility and / or adsorption to the resin constituting the resin particles.

[0078] Examples of resin particles containing a thermochromic material or a photochromic material include: colored resin particles in which a reversible thermochromic composition is uniformly dispersed in resin particles (hereinafter, sometimes referred to as “reversible thermochromic resin particles”); and colored resin particles in which a reversible photochromic composition is uniformly dispersed in resin particles (hereinafter, sometimes referred to as “reversible photochromic resin particles”).

[0079] The resin particles used in the embodiment of the present invention also include solid resin particles without voids inside the particles and hollow resin particles with voids inside the particles.

[0080] The resin particles can be produced by a pulverization method, a spray drying method, or a polymerization method in which a dye, a pigment, a thermochromic material, and / or a photochromic material is polymerized in an aqueous or oily medium. Examples of the polymerization method include suspension polymerization, suspension polycondensation, dispersion polymerization, and emulsion polymerization.

[0081] The shape of the resin particles is not particularly limited, and spherical shapes such as true spheres, ellipsoids, and substantially spheres, polygonal shapes, and flat shapes can be used. Among them, spherical resin particles are preferred.

[0082] The coloring agent may be used alone or in combination of two or more.

[0083] The reversible thermochromic composition or the reversible photochromic composition is preferably encapsulated in microcapsules and used in the form of microencapsulated pigments. This is because the microcapsules can form chemically and physically stable pigments, and the reversible thermochromic composition or the reversible photochromic composition can maintain the same composition and have the same effect under various use conditions.

[0084] The proportion of colorant is not particularly limited. In order to prevent the colorant from agglomerating and / or settling over time and forming good handwriting, the colorant is preferably mixed in the total amount of the ink composition in a range of 1 to 25% by mass, more preferably in a range of 3 to 20% by mass. If the proportion is greater than 25% by mass, the ink discharge property of the writing instrument containing the ink composition is easily reduced, and poor writing such as flying white and flying lines is easily produced. On the other hand, when the proportion is less than 1% by mass, it is difficult to obtain a suitable handwriting concentration as a writing instrument.

[0085] On the other hand, in order to prevent dripping when the writing instrument is stored for a long time with the nib facing downward and to form good handwriting without white spots, the colorant is preferably blended in the total amount of the ink composition in a range of 1 to 35% by mass, more preferably 2 to 30% by mass.

[0086] In the case where the colorant is a reversible color-changing microcapsule pigment or a reversible photochromic microcapsule pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, these colorants are preferably matched in the total amount of ink in a range of 5 to 40% by mass, more preferably 10 to 40% by mass, and further preferably 10 to 30% by mass. If the matching ratio is greater than 40% by mass, the ink discharge of the writing instrument containing the ink composition is reduced, and poor writing such as flying white and flying lines is easily produced. On the other hand, when the matching ratio is less than 5% by mass, it is difficult to obtain the appropriate color change and handwriting concentration as a writing instrument, and it is difficult to fully meet the color change function.

[0087] In the composition using the colorant dissolved in water, dripping is likely to occur particularly when stored under high humidity, so the configuration in the embodiment of the present invention can be effective. Regarding the prevention of dripping, the most effective method is to add the sulfated cellulose fiber described later to the dye-based aqueous ink composition.

[0088] The ink composition according to the embodiment of the present invention contains sulfated cellulose fibers.

[0089] Sulfated cellulose fibers refer to cellulose fibers in which at least a part of the hydroxyl groups in the glucose units constituting cellulose are modified by sulfate among various cellulose fibers.

[0090] The cellulose used as the matrix may be any cellulose, but cellulose having a cellulose I-type crystal structure is widely used as the matrix.

[0091] Examples of the sulfated cellulose fibers include sulfated cellulose fibers having a cellulose I-type crystal structure in which at least a part of hydrogen atoms of a hydroxyl group of the cellulose fibers are substituted with sulfonic groups represented by the following formula (1).

[0092] (-SO3 － ) r ·Z r+ ……(1)

[0093] [where r is a natural number from 1 to 3. When r = 1, Z r+ is at least one selected from the group consisting of hydrogen ions, alkali metal cations, ammonium ions, aliphatic ammonium ions, and aromatic ammonium ions. r+ At least one selected from the group consisting of alkaline earth metal cations and polyvalent metal cations.]

[0094] In other words, the sulfated cellulose fiber substituted with the sulfonic group represented by the above formula (1) may be a sulfated cellulose fiber having a cellulose I type crystal structure, wherein at least a part of the hydroxyl groups of the cellulose fiber are replaced with sulfate groups ((-O-SO3－ )r·Z r+ )replace.

[0095] Sulfated cellulose fibers have sulfonic acid (-SO3 － ), also includes sulfate groups (-O-SO3 － ) and the hydrophilicity is improved, so the dispersibility when dispersed in the ink composition is improved. Moreover, the electron repulsion of the introduced sulfonic group makes it easy to maintain a dispersed state in the ink composition, and a network structure can be formed by the interaction between the sulfated cellulose fibers. As a result, the sulfated cellulose fibers hinder the contact between the colorants in the ink composition and inhibit the aggregation of the colorants, so the colorants can be stably maintained in the ink composition. In addition, the sulfated cellulose fibers also act as a thickener or gelling agent depending on the fiber length, so the colorant can be further stably maintained in the ink composition. That is, the sulfated cellulose fibers can have the effect of improving the dispersion stability of the colorant (hereinafter referred to as "effect 1").

[0096] In addition, in the ink composition of the embodiment of the present invention, it is presumed that the following acts: by using the above-mentioned sulfated cellulose fibers, if the flow of ink stops, the sulfated cellulose fibers near the pen tip (gap) instantly retain the ink through the interaction between the cellulose fibers, and restore the original fluidity with a small load when writing again. Therefore, even in more severe conditions such as long-term storage, storage at high temperature or high humidity, and when the flow path of the pen tip is unexpectedly expanded, it can effectively suppress the dripping and dripping of the ink. In addition, a dispersed state can be formed again with a small load, so that the handwriting does not produce flying white when writing again, and the effect of forming good handwriting from the beginning can be achieved (hereinafter, these effects are referred to as "effect 2").

[0097] In the embodiment of the present invention, the sulfated cellulose fiber can exert at least one of the above-mentioned “effect 1” and “effect 2”.

[0098] Sulfated cellulose fibers have sulfonic acid (-SO3 － ), also includes sulfate groups (-O-SO3 － ) and the hydrophilicity of the fiber is improved, so the dispersibility when dispersed in the aqueous ink is improved. In addition, due to the electron repulsion of the introduced sulfonic groups, agglomeration in the ink does not occur, and the dispersed state is easily maintained, so that the centrifugal treatment during manufacturing and / or the stability of the ink over time can be ensured under normal conditions, and the ink flow path can be closed under the condition that the ink drips.

[0099] At least part of the hydrogen atoms of the hydroxyl groups of cellulose having a cellulose I type crystal structure is replaced by sulfonic acid groups ((-SO3－ ), also includes sulfate groups (-O-SO3 － The sulfated cellulose fibers substituted with the sulfonic acid groups contained in the cellulose fiber can be exemplified by: micrometer-level fibers that have not been subjected to a defibration treatment (a refinement treatment) and nanometer-level fibers that have been subjected to a defibration treatment. In either case, the average fiber width of the sulfated cellulose fibers is preferably in the range of 0.5 to 500 nm.

[0100] The nano-scale sulfated cellulose fibers subjected to the defibration treatment are fine cellulose fibers subjected to the defibration treatment, and therefore can be referred to as sulfated defibrillated cellulose fibers or sulfated fine cellulose fibers (sulfated cellulose nanofibers). From the viewpoint of producing fine sulfated cellulose fibers that maintain a cellulose I-type crystal structure, the average fiber width of the sulfated cellulose fibers is preferably 0.5 nm or more, more preferably 1 nm or more, and even more preferably 2 nm or more.

[0101] Furthermore, from the viewpoint of removing other constituent elements of pulp (bordered pits, vascular elements, etc.) during the production of sulfated cellulose fibers to obtain pure sulfated cellulose fibers, the average fiber width is preferably 500 nm or less, more preferably 100 nm or less.

[0102] It should be noted that in the ink composition of the embodiment of the present invention, in the case of a composition in which the amount of sulfated cellulose fiber in the ink composition is large or a composition using a light-colored colorant, the hue of the sulfated cellulose fiber sometimes affects the hue of the ink composition. Therefore, in order to obtain transparency when the sulfated cellulose fiber is dispersed in water, the average fiber width of the sulfated cellulose fiber is preferably adjusted to 0.5 to 500 nm, and more preferably 1 to 500 nm, 2 to 100 nm, 2 to 30 nm, 2 to 20 nm, and 2 to 10 nm, respectively. By having the average fiber width within the above range, the hue of the sulfated cellulose fiber is not easily affected by the hue of the ink composition, and the ink composition is likely to show the hue derived from the colorant.

[0103] Here, the ink composition using a reversible thermochromic material or a reversible photochromic material as a colorant reversibly changes color from a color-developing state to a color-decolorizing state according to temperature changes or the presence or absence of light irradiation, and is colorless in the color-decolorizing state, so the color of the ink composition is difficult to be visually confirmed. However, if the color of the sulfated cellulose fiber affects the hue of the ink composition, the residual color in the color-decolorizing state becomes larger, and sometimes the color of the ink composition can be visually confirmed even in the color-decolorizing state. Therefore, even when such a colorant is used, it is preferred to obtain transparency when the sulfated cellulose fiber is dispersed in water, and the average fiber width of the sulfated cellulose fiber is preferably within the above range.

[0104] If the average fiber width of the fine cellulose fibers is less than 0.5 nm, the fine cellulose fibers are dissolved in water as cellulose molecules, and thus it is difficult to exhibit the physical properties (strength, rigidity, or dimensional stability) of fine cellulose fibers. On the other hand, if the average fiber width of the fine cellulose fibers is greater than 500 nm, they cannot be said to be fine cellulose fibers, but are just fibers contained in ordinary pulp, and thus it is difficult to obtain the physical properties (transparency, strength, rigidity, or dimensional stability) of fine cellulose fibers, and there is a tendency to easily settle in the ink composition.

[0105] It should be noted that, when sulfated fine cellulose fibers are applied to ink compositions, in addition to the above-mentioned transparency, the dispersibility in water is also very high, the fine cellulose fibers are easily interacted with each other, and the sulfated cellulose fibers are easy to form a dense network structure, so the dispersion stability of the colorant is further improved. In addition, when sulfated fine cellulose fibers are applied to ink compositions, the dispersibility in aqueous media and the followability during ink flow are very high, so the ink dripping suppression effect is more effectively manifested.

[0106] In the past, in order to make the dispersion stability of the colorant good, the following process was carried out: using thickeners such as fine cellulose and / or xanthan gum to make the ink high viscosity. Thus, the cohesion and / or sedimentation of the colorant can be suppressed, but the writing tools that such high viscosity ink can be applied to are accompanied by restrictions. However, the ink composition using sulfated fine cellulose fibers is easy to form a dense network structure through the interaction of fibers as mentioned above, and has a low viscosity compared to the ink composition using the previous thickener alone, and can stably maintain the colorant for a long time. Therefore, the sulfated fine cellulose fibers exert a rheological control effect different from the previous thickener, and play a good effect of making the dispersion stability of the colorant over time. In addition, it can make the ink composition using the previous thickener alone have a low viscosity, so the ink discharge of the writing tool containing the ink composition is improved, and poor writing such as flying white is suppressed, and the writing sense is good, and the color development of the handwriting can be excellent.

[0107] Furthermore, when the ink composition is used in a writing instrument (ballpoint pen) having a ballpoint pen tip, the broken lines of the handwriting can be suppressed, and the writing performance can be improved.

[0108] If the average fiber width of the sulfated fine cellulose fibers is greater than 30 nm, the aspect ratio decreases, and the fibers tend to be less likely to interact with each other. Moreover, if the average fiber width is greater than 30 nm, it is close to 1 / 10 of the wavelength of visible light. When other additives are added to the ink composition, refraction and scattering of visible light are likely to occur at the interface, and there is a tendency for visible light to be scattered and transparency to decrease. Therefore, from the perspective of operability and transparency, the average fiber width of the sulfated fine cellulose fibers is preferably 2 to 30 nm, more preferably 2 to 20 nm, and even more preferably in the range of 2 to 10 nm.

[0109] In particular, from the perspective of transparency, the average fiber width of the sulfated fine cellulose fibers is preferably 20 nm or less, and more preferably 10 nm or less. If the average fiber width is adjusted to 10 nm or less, the scattering of visible light can be further reduced, thereby obtaining sulfated fine cellulose fibers with high transparency, and suppressing unexpected color changes of the ink composition caused by the addition of sulfated fine cellulose fibers. In addition, from the perspective of suppressing dripping, a better effect is also achieved when the average fiber width is 30 nm or less.

[0110] The average fiber width of sulfated cellulose fibers can be measured as follows: the sulfated cellulose fibers are dispersed in a solvent such as pure water to prepare a mixed solution in a manner to achieve a specified concentration, the mixed solution is spin-coated on a silica substrate coated with polyethyleneimine (PEI), and the sulfated cellulose fibers on the silica substrate are observed.

[0111] As an observation method, a scanning probe microscope (e.g., SPM-9700 manufactured by Shimadzu Corporation) can be used. By randomly selecting 20 sulfated cellulose fibers in the obtained observation image, measuring the fiber widths and averaging the fiber widths, the average fiber width of the sulfated cellulose fibers can be obtained.

[0112] The sulfonic acid group ((-SO3 － ), also includes sulfate groups (-O-SO3 － The amount of sulfonic acid groups contained in the sulfonic acid group (sulfonic acid group) introduced can be expressed as the amount of sulfur introduced, and the amount of introduction is not particularly limited as long as the transparency and dispersibility can be maintained to a certain extent.

[0113] For example, the amount of sulfur introduced per 1 g (mass) of sulfated cellulose fiber is preferably higher than 0.42 mmol / g, more preferably higher than 0.42 mmol / g and 9.9 mmol / g or lower, further preferably 0.50 to 9.9 mmol / g, particularly preferably 0.60 to 9.9 mmol / g.

[0114] When the amount of sulfur introduced per 1 g (mass) of sulfated cellulose fiber is 0.42 mmol / g or less, hydrogen bonds between fibers are strong, so there is a tendency for dispersibility to decrease. On the contrary, when the amount of sulfur introduced exceeds 0.42 mmol / g, dispersibility is easily improved, and when it is set to 0.50 mmol / g or more, electron repulsion can be made stronger, so it is easy to stably maintain the dispersed state. On the other hand, the closer the amount of sulfur introduced is to 9.9 mmol / g, the more likely the crystallinity is to decrease, and there is also a tendency for the cost to increase when introducing sulfur.

[0115] Therefore, the amount of sulfur introduced into the sulfated fine cellulose fibers is preferably adjusted to fall within the above range.

[0116] In particular, the amount of sulfur introduced into the sulfated cellulose fibers is preferably higher than 0.42 mmol / g and less than 3.0 mmol / g, more preferably 0.50 to 3.0 mmol / g, and even more preferably 0.50 to 2.0 mmol / g, from the viewpoint of dispersibility of fine fibers constituting the sulfated pulp fibers.

[0117] Furthermore, from the viewpoint of the transparency of the sulfated cellulose fibers, it is preferably adjusted to the same range as the above range.

[0118] The amount of sulfur introduced into the sulfated cellulose fibers can be determined by burning a predetermined amount of the sulfated cellulose fibers and measuring the sulfur content of the combustion product using combustion ion chromatography according to a method in accordance with IEC62321.

[0119] The average fiber length and average fiber width of the sulfated cellulose fibers are not particularly limited as long as they are adjusted so that the fibers can interact with each other easily and so that transparency is easily obtained when dispersed in water.

[0120] The average fiber length of sulfated cellulose fibers can be indirectly expressed by the degree of polymerization.

[0121] The degree of polymerization is preferably 30 or more, more preferably 40 to 1,000, and even more preferably in the range of 40 to 700.

[0122] If the degree of polymerization of the sulfated cellulose fiber is less than 30, the fibers are less likely to interact with each other due to the reduced fiber length. On the other hand, if the degree of polymerization of the sulfated cellulose fiber is greater than 1000, there is a tendency that the dispersibility becomes low, the slurry viscosity during slurrying is too high, and the dispersion stability becomes low. Therefore, the degree of polymerization of the sulfated cellulose fiber is preferably adjusted within the above range. In particular, from the perspective of the ease of interaction between the fibers, the degree of polymerization is preferably adjusted to 40 or more, and from the perspective of dispersibility and operability, the degree of polymerization is preferably adjusted to 1000 or less, and more preferably adjusted to 700 or less.

[0123] The method for measuring the degree of polymerization is not particularly limited, and it can be measured, for example, by the copper ethylenediamine method. Specifically, the degree of polymerization of the sulfated cellulose fibers can be measured by dissolving the sulfated cellulose fibers in a 0.5 M copper ethylenediamine solution and measuring the viscosity of the solution by a viscosity method.

[0124] It should be noted that for fibers whose fiber length can be visually measured, a scanning electron microscope (SEM) can also be used. For example, wet sulfated cellulose fibers can be filtered and desolventized to obtain a fine fiber sheet, which is then freeze-dried in liquid nitrogen and observed under SEM. The average fiber length of 50 observed fibers is calculated to thereby determine the average fiber length.

[0125] In particular, when evaluating the transparency of sulfated cellulose fibers, it is preferred to use a substance that is not turbid when prepared as an aqueous solution, so the turbidity of the aqueous solution can be more appropriately evaluated using the haze value (Haze value) of an aqueous solution of a specific concentration. Specifically, the haze value of a dispersion obtained by dispersing sulfated cellulose fibers in a predetermined concentration can be measured as follows.

[0126] First, a dispersion is prepared in which sulfated cellulose fibers are dispersed in a water-soluble solvent so as to have a solid content concentration of 0.1 to 20% by mass. If the haze value of the dispersion is 20% or less, the sulfated cellulose fibers can be said to be in a state where they can exhibit transparency with little turbidity. On the other hand, if the haze value of the dispersion prepared so as to have a solid content concentration within the above range is higher than 20%, it can be said that the fibers are in a state where they cannot easily exhibit appropriate transparency.

[0127] For example, when the dispersion liquid in which the sulfated cellulose fibers are dispersed is prepared so that the solid content concentration is 0.2 to 0.5% by mass, if the haze value of the dispersion liquid is 20% or less, it can be said that the state of transparency with less turbidity can be appropriately exerted. In particular, from the perspective of being able to appropriately suppress the turbidity of the dispersion liquid when the sulfated cellulose fibers are dispersed at a predetermined concentration, the haze value is more preferably in the range of 15% or less, and further preferably in the range of 10% or less. Therefore, in terms of exerting a transparent state with less turbidity, the sulfated cellulose fibers are preferably prepared so that the haze value of the dispersion liquid prepared so that the solid content concentration is 0.1 to 20% by mass is 20% or less, more preferably 15% or less, and further preferably in the range of 10% or less.

[0128] The water-soluble solvent is not particularly limited, and for example, in addition to the case of using only water, alcohols, ketones, amines, carboxylic acids, ethers, amides, etc. may be used alone or in combination of two or more.

[0129] The haze value can be measured, for example, using a spectroscopic haze meter or a spectrophotometer in accordance with JIS K 7105. In general, as long as the sulfated cellulose fibers are dispersed in the dispersion liquid in a manner to obtain a predetermined solid content concentration, the dispersion liquid is measured using a spectroscopic haze meter or a spectrophotometer in accordance with JIS K 7105, and the haze value of the sulfated cellulose fibers can be obtained. Specifically, it is obtained in the following manner: a spectrophotometer [manufactured by JASCO Corporation, product name: 0V-570] is installed with an integrating sphere [manufactured by JASCO Corporation, product name: ISN-470], and the haze value is measured with reference to JIS K7105, and a quartz cuvette to which pure water is added is used as a blank measurement value, and the transmittance of a 0.5% by mass sulfated cellulose fiber dispersion liquid is measured. It should be noted that the measurement wavelength range is set to 380 to 780 nm.

[0130] The method for producing the sulfated cellulose fibers is not particularly limited, and for example, known production methods described in Japanese Patent Application Publication No. 2019-11411, Japanese Patent No. 6582111, Japanese Patent No. 6797215, etc. can be applied.

[0131] In particular, as described in Japanese Patent No. 6582111, first, a pulp fiber raw material containing cellulose such as wood is contacted with a reaction solution prepared by dissolving a sulfonating agent such as aminosulfonic acid and urea or / and its derivatives in water (impregnation), and the wet pulp fiber is heated and adjusted to 100 to 180° C. for more than 5 minutes to react, thereby introducing sulfonic groups into at least a part of the hydrogen atoms of the hydroxyl groups of the cellulose fiber (i.e., at least a part of the hydroxyl groups is sulfated) (chemical treatment step). Then, a low-pressure homogenizer, a high-pressure homogenizer, a grinder (a mortar-type pulverizer), a ball mill, a shredder, a jet mill, a single-screw extruder, a twin-screw extruder, an ultrasonic stirrer, a household mixer, etc. are used to make fine fibers of a predetermined size (fine processing step), thereby manufacturing sulfated cellulose fibers.

[0132] The use of such a method is particularly preferred because it is possible to efficiently produce sulfated fine cellulose fibers having an average fiber width of the nanometer order.

[0133] The blending ratio of the sulfated cellulose fibers is not particularly limited, but the sulfated cellulose fibers are preferably blended in an amount of 0.01 to 3% by mass, more preferably 0.05 to 1% by mass, based on the total amount of the ink composition.

[0134] When the amount is less than 0.01% by mass, it is difficult to obtain the desired effect of stably maintaining the colorant in a dispersed state, and it is also difficult to obtain the desired anti-drip effect. On the other hand, even if the amount is greater than 3% by mass, it is difficult to achieve an improvement in the dispersion stability effect. Furthermore, even if an amount greater than 3% by mass is added, the anti-drip effect cannot be improved, so further addition is not necessary.

[0135] The average particle size of the colorant is not particularly limited, but is preferably in the range of 0.01 to 25 μm, more preferably 0.05 to 20 μm. When the average particle size of the colorant is within the above range, the dispersion stability in the ink composition is excellent, and handwriting of a desired color is easily obtained.

[0136] It should be noted that the average particle size is measured by using image analysis particle size distribution measurement software [Mountech Co., Ltd., product name: Mac-View] to determine the area of ​​the particles, and calculate the projected area equivalent circle diameter (Heywood diameter) based on the area of ​​the particle area, and the value measured is the average particle size of the particles equivalent to a sphere of equal volume based on this value.

[0137] When the particle size of all or most particles is larger than 0.2 μm, the particle size distribution can be measured as the average particle size of particles equivalent to a sphere of equal volume by the Coulter method using a particle size distribution analyzer [Beckman Coulter Co., Ltd., product name: Multisizer 4e].

[0138] Furthermore, the volume-based particle size and average particle size may be measured using a calibrated laser diffraction / scattering particle size distribution measuring apparatus [manufactured by Horiba, Ltd., product name: LA-300] based on the values ​​measured using the above-mentioned software or a measuring apparatus utilizing the Coulter method.

[0139] In the ink composition of the embodiment of the present invention, as a colorant, a colorant having a large average particle size (hereinafter sometimes referred to as "large particle size colorant") such as a reversible thermochromic microcapsule pigment and / or a reversible photochromic microcapsule pigment, a bright pigment, etc. may be used.

[0140] Colorants with large average particle sizes tend to settle over time in ink compositions, and sometimes have poor dispersion stability. In particular, when the ink composition has low viscosity, there is a tendency for the dispersion stability to deteriorate further. However, the ink composition of an embodiment of the present invention can suppress the sedimentation of large-particle-size colorants over time by using the sulfated cellulose fibers, and the large-particle-size colorants exhibit good dispersion stability. In addition, when sulfated fine cellulose fibers are used, the ink composition can be made low-viscosity, and the large-particle-size colorants can be stably dispersed for a long time.

[0141] The bright pigment is not particularly limited as long as it exhibits bright properties by reflecting light, and examples thereof include naturally occurring pigments such as fish scales, pigments obtained by coating a transparent base with a metal oxide or metal, and metallic pigments.

[0142] Examples of pigments formed by coating a transparent substrate with a metal oxide include: a pigment formed by using a material selected from natural mica, synthetic mica, flat glass (sheet glass), silica flakes, flaky alumina, etc. as a substrate and coating the surface of the substrate with a metal oxide.

[0143] Examples of the metal oxide include oxides of titanium, zirconium, chromium, vanadium, iron, and the like, and titanium oxide is preferred.

[0144] In addition, depending on the coverage of the metal oxide on the surface of the coated substrate and the thickness of the coating, the color may be gold or silver, or yellow, red, blue or green with a metallic luster. It should be noted that the pigment may be a non-color-changing colorant such as iron oxide and / or a common dye or pigment further coated on the layer of metal oxide such as titanium oxide.

[0145] Pigments obtained by coating a transparent base material with a metal oxide also include pearlescent pigments and cholesteric liquid crystal pigments.

[0146] Examples of pigments formed by coating a transparent substrate with a metal include pigments formed by coating flaky glass with silver, pigments formed by coating flaky glass with gold, pigments formed by coating flaky glass with nickel-chromium-molybdenum, pigments formed by coating flaky glass with brass, pigments formed by coating flaky glass with a silver alloy, and pigments formed by coating flaky glass with titanium.

[0147] The pigment in which a transparent base material is coated with a metal can be obtained by, for example, applying the metal to a glass sheet by chemical plating or sputtering.

[0148] As the metal pigment, for example, an aluminum powder pigment can be exemplified.

[0149] As an example of aluminum powder pigment, for example, aluminum powder pigment obtained by crushing and grinding aluminum flakes with a petroleum solvent such as a higher fatty acid or mineral spirits using a ball mill can be exemplified. Such aluminum powder pigment is very thin flaky aluminum particles, and the aluminum powder pigment obtained in a paste form can be used.

[0150] Alternatively, an aluminum powder pigment may be one obtained by finely pulverizing thin-film aluminum obtained by vacuum deposition.

[0151] The average particle size of the reversible thermochromic microcapsule pigment or the reversible photochromic microcapsule pigment is preferably 0.1 to 5 μm, more preferably 0.5 to 4 μm, and even more preferably 0.5 to 3 μm. If the average particle size is greater than 5 μm, it is difficult to obtain good ink discharge properties when used in writing tools. On the other hand, when the average particle size is less than 0.1 μm, it is difficult for the handwriting to show high-concentration color development.

[0152] The average particle size of the bright pigment is preferably 3 to 25 μm, more preferably 5 to 20 μm. If the average particle size is greater than 25 μm, it is difficult to obtain good ink discharge properties when used in writing instruments. On the other hand, when the average particle size is less than 3 μm, it is difficult for the handwriting to show sufficient brightness.

[0153] The specific gravity of the colorant is not particularly limited, and in the ink composition of the embodiment of the present invention, a colorant having a specific gravity greater than 1 (hereinafter sometimes referred to as a "high specific gravity colorant") may be used as the colorant. That is, the embodiment of the present invention may also include a colorant having a specific gravity greater than 1 (or at least a part of the colorant may have a specific gravity greater than 1).

[0154] Colorants with a specific gravity greater than 1 tend to settle over time in ink compositions, and sometimes have poor dispersion stability. In particular, when the ink composition has a low viscosity, there is a tendency for the dispersion stability to deteriorate further. However, the ink composition of an embodiment of the present invention can suppress the sedimentation of a high-specific gravity colorant over time by using the sulfated cellulose fibers, and the high-specific gravity colorant exhibits good dispersion stability. In addition, when sulfated fine cellulose fibers are used, the ink composition can be made low-viscosity, and the high-specific gravity colorant can be stably dispersed for a long time.

[0155] Examples of high specific gravity colorants include inorganic pigments, organic pigments, bright pigments, or microcapsule pigments or resin particles using these pigments, and reversible thermochromic microcapsule pigments having a large hysteresis width (ΔH).

[0156] Examples of the organic pigment include benzidine yellow, permanent red, lake red, Victoria blue lake, phthalocyanine blue, phthalocyanine green, and aniline black, etc. The specific gravity is in the range of 1.2 to 2.9.

[0157] Examples of the inorganic pigment include carbon black, ultramarine blue, rutile type / anatase type titanium oxide, etc. The specific gravity of carbon black and ultramarine blue is in the range of 1.4 to 5.5, and that of titanium oxide is in the range of 3.7 to 4.2.

[0158] Examples of the bright pigment include pigments obtained by coating a transparent base material with the above-mentioned metal oxide or metal, and metallic pigments.

[0159] The specific gravity of a pigment obtained by coating a transparent substrate with a metal oxide is in the range of 2.8 to 3.2 for pearlescent pigments and in the range of 1.1 to 1.5 for cholesteric liquid crystal pigments.

[0160] The specific gravity of the pigment obtained by coating a transparent base material with a metal is in the range of 3.0 to 3.4.

[0161] The specific gravity of the metallic pigment is in the range of 2.5 to 9.0.

[0162] Reversible thermochromic microcapsule pigments having a large hysteresis width often use a compound having two or more aromatic rings in the molecule as the component (C), and the specific gravity tends to be large.

[0163] The specific gravity of the reversible thermochromic microcapsule pigment is affected by the particle size, the components encapsulated in the microcapsule and their content, the components and thickness of the capsule wall membrane, the coloring state of the microcapsule pigment, and the temperature. From the viewpoint of dispersion stability in the ink composition, the specific gravity of the reversible thermochromic microcapsule pigment is preferably 1.05 to 1.20, more preferably 1.10 to 1.20, and even more preferably 1.12 to 1.15 when the microcapsule pigment is in a fully colored state and water is used as a reference substance under an environment of 20°C.

[0164] It should be noted that the specific gravity of the reversible thermochromic microcapsule pigment can be measured by the following method.

[0165] (Method for determining specific gravity of reversible thermochromic microcapsule pigments)

[0166] 1. Add 30 ml of glycerol aqueous solution and 1 g of reversible thermochromic microcapsule pigment in a fully colored state into a screw-capsule bottle and mix them to prepare a microcapsule pigment dispersion.

[0167] 2. Adjust the temperature of 30 ml of microcapsule pigment dispersion to 20°C and place it in a centrifuge at 1000 rpm for 30 seconds. It should be noted that as a centrifuge, a cooling-table centrifuge (manufactured by Kokusan Co., Ltd., product name: H103N) can be used.

[0168] 3. Observe the microencapsulated pigment dispersion.

[0169] When most of the microcapsule pigment is precipitated at the bottom of the beaker, operations 1 and 2 are repeated using an aqueous solution having a higher glycerin concentration than the current glycerin aqueous solution, and the state of the dispersion is observed.

[0170] When it is confirmed that most of the microcapsule pigments are floating on the liquid surface, operations 1 and 2 are repeated using an aqueous solution having a lower glycerin concentration than the current glycerin aqueous solution, and the state of the dispersion is observed.

[0171] The above series of operations are repeated until it is visually confirmed that the portion other than the liquid surface of the glycerin aqueous solution and the bottom of the screw-cap bottle is uniformly colored, rather than the microcapsule pigment mostly floating to the liquid surface or precipitating. The specific gravity of the glycerin aqueous solution when this state is observed is measured as the specific gravity of the reversible thermochromic microcapsule pigment. It should be noted that the specific gravity of the glycerin aqueous solution can be measured by the buoy method described in JIS K00617.1, which is an aqueous solution adjusted to 20°C.

[0172] The specific gravity of the high specific gravity colorant is preferably in the range of 1.01 to 5.00, more preferably 1.05 to 4.50.

[0173] The ink composition of the embodiment of the present invention may contain a thickener. By using the sulfated cellulose fiber and the thickener together, the viscosity is lower than that of the conventional ink composition using only the thickener, and the colorant can be stably maintained in a dispersed state for a long period of time.

[0174] As the thickener, it is preferred to use a substance that can impart shear-thinning properties to the ink composition (a shear-thinning property-imparting agent).

[0175] The ink composition using the shear-thinning agent has high viscosity and is difficult to flow when it is static or under low stress, and easily becomes less viscous when stress is applied from the outside. Therefore, when not writing, it is possible to prevent the ink from leaking out or preventing the ink from separating and flowing back, and when writing, it is easy to make the ink discharge from the pen tip stable.

[0176] When the ink composition according to the embodiment of the present invention contains a thickener, the blending ratio of the thickener is not particularly limited, but the thickener is preferably blended in an amount within a range of 0.1 to 20% by mass based on the total amount of the ink composition.

[0177] As the shear-thinning agent, for example, there can be exemplified any one or more selected from the group consisting of water-soluble polysaccharides, polymers having a molecular weight of 100,000 to 150,000 and containing an alkyl ester of methacrylic acid as a main component, poly-N-vinylcarboxylic acid amide crosslinked products, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali thickening type acrylic resins, crosslinked acrylic polymers, inorganic fine particles, nonionic surfactants having an HLB value of 8 to 12, and metal salts or amine salts of dialkyl sulfosuccinic acids.

[0178] It should be noted that the shear thinning property of ink refers to the property that it has high viscosity and is not easy to flow when it is static or under low stress. If the stress increases, the viscosity decreases and it exhibits good fluidity. This is a rheological property also called thixotropy or pseudoplasticity.

[0179] When the ink composition according to the embodiment of the present invention contains a shear thinning agent, the blending ratio of the shear thinning agent is not particularly limited, but the shear thinning agent is preferably blended in a range of 0.05 to 1% by mass based on the total amount of the ink composition.

[0180] Examples of water-soluble polysaccharides include xanthan gum, welan gum, zetashi gum, diutan gum, Macrophomopsis gum, succinoglycan (e.g., succinoglycan (average molecular weight of about 1 million to 8 million) as an organic acid-modified heteropolysaccharide whose structural monosaccharides are glucose and galactose), guar gum, locust bean gum and its derivatives, alginic acid alkyl esters, glucomannan, agar, and carbohydrates extracted from seaweeds such as carrageenan that have gelling ability. It should be noted that water-soluble cellulose derivatives including hydroxyethyl cellulose can also belong to water-soluble polysaccharides, but in the present disclosure, water-soluble cellulose derivatives including hydroxyethyl cellulose do not belong to water-soluble polysaccharides (i.e., shear-thinning agents) but belong to the polymer coagulants described later.

[0181] As the thickener (shear-thinning agent) used together with the sulfated cellulose fibers, xanthan gum or succinoglycan is preferred because it can further improve the dispersion stability of the colorant.

[0182] The shear-thinning agent may be used alone or in combination of two or more.

[0183] A polymer coagulant may be added to the ink composition of the embodiment of the present invention. By adding a polymer coagulant, the colorant forms a loose aggregate via the polymer coagulant, and the colorants are prevented from contacting each other and agglomerating, thereby improving the dispersibility of the colorant. In addition, by using a polymer coagulant and sulfated cellulose fibers together, the colorant can be stably retained in the ink composition, so the amount of sulfated cellulose fibers added in the ink composition can be reduced.

[0184] When the ink composition according to the embodiment of the present invention contains a polymer flocculant, the blending ratio of the polymer flocculant is not particularly limited, but the polymer flocculant is preferably blended in an amount within a range of 0.05 to 1% by mass based on the total amount of the ink composition.

[0185] Examples of the polymer coagulant include polyvinyl pyrrolidone, polyethylene oxide, and water-soluble cellulose derivatives.

[0186] Examples of the water-soluble cellulose derivative include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

[0187] When the ink composition of the embodiment of the present invention is used for a writing instrument (ballpoint pen) having a ballpoint pen tip, a lubricant may be added to the ink composition. The lubricant can improve the lubricity of the ball holder provided inside the pen tip body and the ball provided at the front end of the pen tip body, easily prevent the wear of the ball holder, and improve the writing feel.

[0188] Examples of lubricants include: higher fatty acids such as oleic acid; nonionic surfactants having long-chain alkyl groups; polyether-modified silicone oils; thiophosphite triesters such as tris(alkoxycarbonylmethyl) thiophosphite and tris(alkoxycarbonylethyl) thiophosphite, phosphoric acid monoesters of polyoxyethylene alkyl ethers or polyoxyethylene alkyl aryl ethers, phosphoric acid diesters of polyoxyethylene alkyl ethers or polyoxyethylene alkyl aryl ethers, or phosphoric acid ester surfactants such as metal salts, ammonium salts, amine salts, and alkanolamine salts of these phosphoric acid esters. In addition, metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide addition type cationic surfactants, β-alanine type surfactants, N-acylamino acids, N-acylmethyltaurine, 2,5-dimercapto-1,3,4-thiadiazole and its salts or oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamates, dimethyldithiocarbamates, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine and its salts can also be used.

[0189] The ink composition of the embodiment of the present invention may also be mixed with various additives such as a water-soluble organic solvent, a dispersant, a water-soluble resin, a surfactant, a pH adjuster, a rust inhibitor, a preservative or a mildew inhibitor, a wetting agent, a bubble absorber, a defoamer, a specific gravity adjuster, an antioxidant, and a UV absorber as needed. These additives can be selected from additives conventionally used in water-based inks and used appropriately.

[0190] When the colorant is a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, it is also possible to prepare an ink composition that exhibits a color change behavior from colored (1) to colored (2) by combining it with a non-color-changing colorant such as a conventional dye or pigment.

[0191] The method for producing the ink composition according to the embodiment of the present invention is not particularly limited, and any conventionally known method may be used.

[0192] Specifically, the ink composition can be produced by stirring a mixture containing the above-mentioned components with various stirrers such as a propeller stirrer, a homodisperser, or a homomixer, or by dispersing the mixture with various dispersers such as a bead mill.

[0193] When the ink composition of the embodiment of the present invention is used in a ballpoint pen, the ink composition is subjected to rotation at a speed of 1 rpm (shear rate of 3.84 sec －1 ), the viscosity of the ink composition is preferably in the range of 1 to 2000 mPa·s, more preferably in the range of 3 to 1500 mPa·s, and even more preferably in the range of 5 to 1000 mPa·s. In addition, under an environment of 20°C, at a rotation speed of 100 rpm (shear speed of 384 sec －1 ), the viscosity of the ink composition is preferably 1 to 200 mPa·s, more preferably 3 to 100 mPa·s, and even more preferably 5 to 50 mPa·s. By keeping the viscosity within the above range, the stability of the ink composition and the fluidity of the ink composition in the mechanism of the ballpoint pen can be maintained at a high level.

[0194] The viscosity of the ink composition was measured using a rheometer [manufactured by TA Instruments, product name: Discovery HR-2, cone and plate (diameter 40 mm, angle 1°)], in which the ink was placed in an environment of 20°C and rotated at a speed of 1 rpm (shear rate 3.84 sec －1 ) or rotation speed 100rpm (shear speed 384sec －1 ) under the conditions of

[0195] When the ink composition of the embodiment of the present invention is used for a marker pen, the viscosity of the ink composition is preferably 1 to 30 mPa·s, more preferably 1 to 20 mPa·s, and even more preferably 1 to 10 mPa·s when measured at 20°C and 20 rpm. When the viscosity is within the above range, the stability and fluidity of the ink composition can be maintained at a high level.

[0196] The viscosity of the ink composition is a value measured by placing the ink composition in an environment of 20° C. using an E-type rotational viscometer [manufactured by Toki Sangyo Co., Ltd., product name: RE-85L, cone rotor: standard type (1°34′×R24)].

[0197] The pH of the ink composition according to the embodiment of the present invention is preferably in the range of 6 to 10, and more preferably in the range of 7 to 9. When the pH is in the above range, excessive increase in viscosity and deterioration of the ink composition can be suppressed.

[0198] The pH of the ink composition is a value measured by placing the ink in an environment of 20° C. using a pH meter [manufactured by DKK-TOA Co., Ltd., product name: IM-40S].

[0199] Examples of writing instruments that contain the ink composition according to the embodiment of the present invention include various writing instruments such as ballpoint pens, marker pens, fountain pens, and calligraphy pens.

[0200] When the ink composition of the embodiment of the present invention is used in a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited, and the ink composition can be used by filling a ballpoint pen refill or a ballpoint pen having a ballpoint pen tip and an ink filling mechanism.

[0201] The ballpoint pen tip includes a pen tip body and a ball at the front end of the pen tip body. Examples of the ballpoint pen tip include a pen tip having a ball held in a ball holding portion formed by pressing and deforming the pen tip body formed of a metal tube from the outer surface to the inner side, a pen tip having a ball held in a ball holding portion formed by cutting a pen tip body formed of a metal material using a drill, a pen tip having a resin ball holder provided inside a metal or plastic pen tip body, or a pen tip having a ball held by the above pen tip urged forward by a spring.

[0202] The material of the nib body and the ball is not particularly limited, and examples thereof include cemented carbide (superhard), stainless steel, ruby, ceramic, resin, rubber, etc. Furthermore, the ball may be subjected to surface treatment such as DLC coating.

[0203] The diameter of the ball is usually 0.1 to 3 mm or 0.2 to 3 mm, preferably 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, 0.28 to 1 mm.

[0204] It should be noted that the ballpoint pen tip can also be constructed as follows: a pop-up component is arranged in the pen tip to pop up the rear end of the ball forward, so that the ball is pressed to the inner edge of the front end of the pen tip and is in close contact when not writing. When writing, the ball is moved backward by the pen pressure to allow the ink to flow out, thereby preventing ink leakage when not in use.

[0205] Examples of the spring member include a spring of a metal thin wire, a member having a standing portion (rod) at one end of the spring, and a linear plastic processed body, and the structure is configured to be applied by being pressed by an elastic force of 5 to 40 g.

[0206] As the ink filling mechanism, for example, an ink container that can be directly filled with ink can be exemplified.

[0207] The ink container may be a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body.

[0208] By connecting the ballpoint pen tip directly or via a connecting member to the ink container and directly filling the ink container with ink, a ballpoint pen refill (hereinafter sometimes referred to as "refill") can be formed. By accommodating the refill in the pen barrel, a ballpoint pen can be formed.

[0209] The ink repellent reverse fluid is filled at the rear end of the ink filled in the ink container. As the ink repellent reverse fluid, a liquid plug or a solid plug can be cited.

[0210] The liquid plug is formed of a non-volatile liquid and / or a hardly volatile liquid, for example, vaseline, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, oligomers or co-oligomers of α-olefin, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc.

[0211] The nonvolatile liquid and / or the low-volatile liquid may be used alone or in combination of two or more.

[0212] It is preferred to add a thickener to the nonvolatile liquid and / or the low-volatile liquid to increase the viscosity to an appropriate level.

[0213] Examples of thickeners include: clay-based thickeners such as silica with a hydrophobic surface treatment, microparticle silica with a methylated surface treatment, aluminum silicate, expanded mica, hydrophobic bentonite and montmorillonite; fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate; dextrin-based compounds such as tribenzylidene sorbitol, fatty acid amide, amide-modified polyethylene wax, hydrogenated castor oil, and fatty acid dextrin; cellulose-based compounds, etc.

[0214] Examples of the solid plug include a solid plug made of polyethylene, polypropylene, polymethylpentene, and the like.

[0215] As the ink repellent backflow fluid, a solid plug and the above-mentioned liquid plug may be used in combination.

[0216] In addition, the pen barrel itself can also be used as the ink filling mechanism, ink can be directly filled into the pen barrel, and a ballpoint pen tip can be attached to the front end of the pen barrel, thereby forming a ballpoint pen with a ballpoint pen tip and an ink filling mechanism.

[0217] When the ink filled in the ink filling mechanism has a low viscosity, the ballpoint pen including the ballpoint pen tip and the ink filling mechanism may further include an ink supply mechanism for supplying the ink filled in the ink filling mechanism to the pen tip.

[0218] The ink supply mechanism is not particularly limited, and examples thereof include the following mechanisms: (1) a mechanism having an ink guide core formed of a fiber bundle as an ink flow regulator, and supplying ink to the pen tip in a manner of sandwiching the ink flow regulator; (2) a mechanism having a comb-groove-shaped ink flow regulator, and supplying ink to the pen tip in a manner of sandwiching the ink flow regulator; (3) a mechanism in which a plurality of disk bodies are arranged side by side with comb-groove-shaped intervals, a slit-shaped ink guide groove that runs longitudinally through the disk body in the axial direction and a ventilation groove that is larger than the width of the groove, an ink guide core for guiding ink from the ink filling mechanism to the pen tip is arranged at the axis center to form a pen core, and ink is supplied to the pen tip via the pen core.

[0219] The material of the refill is not particularly limited as long as it is a synthetic resin that can be injection molded into a comb-shaped structure with multiple disc bodies. From the perspective of high moldability and easy to obtain refill performance, acrylonitrile-butadiene-styrene copolymer (ABS resin) is preferably used.

[0220] As the structure of a ballpoint pen that contains the ink composition of an embodiment of the present invention, specifically, the following ballpoint pens can be exemplified: (1) a ballpoint pen having an ink container filled with ink in a pen body, a ballpoint pen tip connected to the ink container directly or via a connecting member, and an ink backflow-proof fluid filled on the end face of the ink; (2) a ballpoint pen having the following mechanism: a mechanism in which the pen body is directly filled with ink, a comb-shaped ink flow regulating body or an ink guide core composed of a fiber bundle or the like is sandwiched as an ink flow regulating body, and ink is supplied to the pen tip; (3) a ballpoint pen having the following mechanism: a mechanism in which the pen body is directly filled with ink, and ink is supplied to the pen tip via the above-mentioned pen core.

[0221] When the ink composition according to the embodiment of the present invention is used in a marking pen, the structure and shape of the marking pen itself are not particularly limited, and the composition may be used by filling a marking pen refill or a marking pen having a marking pen tip and an ink filling mechanism.

[0222] As the marking pen tip, for example, there can be shown: a porous member with interconnected pores in the porosity range of about 30 to 70% selected from resin processed bodies of fibers, fusion processed bodies of heat-soluble fibers, felt bodies, etc. that have been commonly used; or an extruded body of a synthetic resin having a plurality of ink outlet holes extending in the axial direction, etc., one end of which is processed into a shape corresponding to the purpose, such as a shell shape, a rectangular shape, a chisel shape, etc. for practical use.

[0223] As the ink filling mechanism, for example, an ink storage body that can be filled with ink can be exemplified.

[0224] The ink storage body is a fiber bundle formed by bundling crimped fibers in the longitudinal direction, and is configured to be built in a covering body such as a plastic rod or a film, and the porosity is adjusted to a range of approximately 40 to 90%.

[0225] The marking pen can be formed by accommodating an ink storage body impregnated with ink in a pen body, and connecting the marking pen tip to the pen body directly or via a connecting member so as to be connected to the ink storage body.

[0226] In addition, by accommodating an ink occlusion body impregnated with ink in the ink container, and connecting the marker pen tip to the ink container directly or via a connecting member in a manner connected to the ink occlusion body, a marker pen refill (hereinafter sometimes referred to as a "refill") can be formed. By accommodating the refill in the pen holder, a marker pen can be formed.

[0227] As the ink container, for example, a molded body formed of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body is used.

[0228] The marking pen including the marking pen tip and the ink filling mechanism may further include an ink supply mechanism for supplying the ink composition filled in the ink filling mechanism to the pen tip.

[0229] The ink supply mechanism is not particularly limited, and for example, in addition to the ink supply mechanism of the above-mentioned ballpoint pen, there can be listed: (4) an ink flow regulator based on a valve mechanism, which supplies ink to the pen tip by opening the valve, etc.

[0230] The valve mechanism may use a conventionally used pump-type valve mechanism that is opened by pressing the pen tip, and is preferably set to a spring pressure that can be pressed open by writing pressure.

[0231] When the marking pen has an ink supply mechanism, in addition to using the above-mentioned ink occlusion body, an ink container that can be directly filled with ink can be used as the ink filling mechanism. In addition, the pen itself can be used as the ink filling mechanism to directly fill the ink.

[0232] As the structure of a marking pen that contains the ink composition of an embodiment of the present invention, specifically, the following marking pens can be exemplified: (1) a marking pen in which an ink storage body composed of a fiber bundle impregnated with ink is stored in a pen body, and a marking pen tip composed of a fiber processed body or a resin molded body with capillary gaps is connected to the pen body directly or via a connecting member in such a way that the ink storage body and the pen tip are connected; (2) a marking pen having the following mechanism: the pen body is directly filled with ink, a comb-groove-shaped ink flow regulating body or a structure in which an ink guide core composed of a fiber bundle or the like is sandwiched as an ink flow regulating body, and a mechanism for supplying ink to the pen tip; (3) a marking pen having the following mechanism: the pen body is directly filled with ink, and the ink is supplied to the pen tip via the above-mentioned pen core; (4) a marking pen having a pen tip and an ink storage body via a valve mechanism that opens the valve by pressing the pen tip, and the ink storage body is directly filled with ink.

[0233] In the case where the ballpoint pen or marker of the embodiment of the present invention is directly filled with ink, in order to facilitate the redispersion of the colorant, a stirring body such as a stirring ball for stirring the ink may be built into the ink container or the pen holder for filling the ink. The shape of the stirring body may include a spherical body, a rod-shaped body, etc. The material of the stirring body is not particularly limited, and examples thereof include metal, ceramic, resin, glass, etc.

[0234] The writing tools such as the ballpoint pen or the marking pen of the embodiment of the present invention can also adopt the ink cartridge form as a detachable structure. In this case, by replacing with a new ink cartridge after exhausting the ink contained in the ink cartridge of the writing tool, the writing tool can be used again.

[0235] As the ink cartridge, an ink cartridge that is connected to the pen body and serves as the pen holder of the pen, or an ink cartridge that covers and protects the pen holder (rear holder) after being connected to the pen body can be used. It should be noted that in the latter, in addition to using the ink cartridge alone, the ink cartridge can be connected to the pen body before use, or the ink cartridge can be stored in the pen holder in a non-connected state, such as when the user of the pen uses the pen, the ink cartridge in the pen holder is connected and used.

[0236] In a writing instrument such as a ballpoint pen or a marker pen according to an embodiment of the present invention, a cap-type writing instrument is formed by providing a cap attached so as to cover the pen tip (writing tip), thereby preventing the writing tip from being contaminated or damaged.

[0237] In addition, in a writing instrument such as a ballpoint pen or a marker pen that contains a refill in the pen barrel, a telescopic mechanism that can extend and retract the writing tip from the pen barrel can be provided in the pen barrel to make a telescopic writing instrument, which can prevent the writing tip from being contaminated or damaged. A telescopic writing instrument (such as a telescopic ballpoint pen) is a state where the pen tip is always exposed to the outside air, so the ink composition of an embodiment of the present invention is particularly effective.

[0238] Any retractable writing instrument can be used as long as the writing tip is housed in the pen body in a state exposed to the outside air, and the writing tip protrudes from the pen body opening by the operation of the retractable mechanism.

[0239] In addition, a composite telescopic writing instrument can be made in which a plurality of refills are housed in the pen body, and the writing tip of any refill can be extended and retracted from the opening of the pen body by the operation of the telescopic mechanism.

[0240] As examples of telescopic mechanisms, the following telescopic mechanisms can be exemplified: (1) a side-sliding telescopic mechanism in which an operating portion (pen clip) is provided protruding radially outward and movable along the rear side wall of the pen barrel in the front-to-rear direction, and the operating portion is slid forward to allow the writing tip portion to be telescoped from the front end opening of the pen barrel; (2) a rear-end push-type telescopic mechanism in which an operating portion provided at the rear end of the pen barrel is pressed forward to allow the writing tip portion to be telescoped from the front end opening of the pen barrel; (3) a side-push-type telescopic mechanism in which an operating portion protruding from the outer surface of the side wall of the pen barrel is pressed radially inward to allow the writing tip portion to be telescoped from the front end opening of the pen barrel; (4) a rotating telescopic mechanism in which an operating portion at the rear of the pen barrel is rotated to allow the writing tip portion to be telescoped from the front end opening of the pen barrel.

[0241] The shape of ballpoint pens and marker pens is not limited to the above-mentioned structure. In addition to nibs of different shapes being attached or nibs being attached that output ink of different tones or hues, there may also be composite pens (double-headed and nib-dispensing types, etc.) that have nibs of different shapes attached and the tones or hues of the ink outputted from each nib being different.

[0242] As a writing instrument containing the ink composition of the embodiment of the present invention, it is preferably a writing instrument (ballpoint pen) having a ballpoint pen tip as the form of a pen tip. The ink composition of the embodiment of the present invention is high viscosity when standing without applying shear stress, so the ink composition is stably maintained in a ballpoint pen, and the dispersion stability of the colorant is good. Moreover, when writing, a strong shear stress is applied to the ink composition by the rotation of the ball, and the ink composition near the ball is more easily low-viscosity, so the ink discharge stability is good. That is, from the aspect of suppressing poor writing such as flying white and / or flying lines and good writing sense, and the color development of the handwriting is excellent, the ink composition of the embodiment of the present invention is preferably used for a ballpoint pen. Moreover, from the aspect of the lack of ink retention at the pen tip of the ballpoint pen tip, it is easy to drip and droop, and the ink composition of the embodiment of the present invention is also preferably used for a ballpoint pen.

[0243] When reversibly thermochromic microcapsule pigments or reversibly thermochromic resin particles are used as colorants, handwriting formed on a writing surface using a writing instrument containing an ink composition according to an embodiment of the present invention can change color by rubbing with fingers, heating a tool, and / or cooling a tool.

[0244] As heating tools, there are: electric heating color-changing tools equipped with resistance heating elements such as PTC elements, heating color-changing tools filled with media such as warm water, heating color-changing tools using steam and laser, the use of hair dryers, etc. From the perspective of being able to change color by a simple method, friction components and friction bodies are preferred.

[0245] Examples of the cooling tool include an electrically conductive thermochromic tool using a Peltier element, a thermochromic tool filled with a refrigerant such as cold water or ice flakes, and applications of a refrigerant, a refrigerator, and a freezer.

[0246] As the friction member and the friction body, preferably, an elastic body such as an elastic body having a strong elasticity and capable of generating friction heat by moderate friction when rubbing, a plastic foam body, etc., can also be used. It should be noted that a common eraser for erasing pencil marks can also be used to erase the marks, but eraser crumbs are generated when rubbing, so it is preferred to use the above-mentioned friction member and the friction body that hardly generate eraser crumbs.

[0247] Examples of materials for the friction member and the friction body include silicone resin, styrene-ethylene-butadiene-styrene block copolymer (SEBS resin), etc. Since silicone resin easily adheres to the portion removed by rubbing, and the handwriting is repelled when writing repeatedly, SEBS resin is more preferably used.

[0248] The friction member or friction body can be a member of any shape that is separate from the writing tool, and can be made into an object with excellent portability by being arranged on the writing tool. In addition, the writing tool and the friction member or friction body of any shape that is separate from the writing tool can also be combined to obtain a writing tool kit.

[0249] In the case of a writing instrument with a pen cap, the location where the friction component or friction body is provided is not particularly limited. For example, the pen cap itself can be formed by the friction component, or the pen body itself can be formed by the friction component, or when a pen clip is provided, the pen clip itself can be formed by the friction component, or the friction component or friction body can be provided at the front end (top) of the pen cap or the rear end of the pen body (the part where the writing front end is not provided).

[0250] In the case of a writing instrument with a telescopic mechanism, the location where the friction component or friction body is provided is not particularly limited. For example, the pen body itself may be formed by the friction component, or the pen clip itself may be formed by the friction component when a pen clip is further provided, or the friction component or friction body may be provided near the opening of the pen body, at the rear end of the pen body (the part where the writing front end is not provided), or at the pressing part.

[0251] Example

[0252] Examples are shown below, but the embodiments of the present invention are not limited thereto. It should be noted that "parts" in Examples mean "parts by mass" unless otherwise specified.

[0253] [Example 1]

[0254] The following Example 1 shows that the ink composition according to the embodiment of the present invention and the colorant of the writing instrument containing the ink composition are unlikely to aggregate and / or precipitate over time, and can form good handwriting.

[0255] Preparation of ink composition (Example 1-1)

[0256] An ink composition was prepared by mixing 30 parts of a blue pigment aqueous dispersion (Pigment Blue 15:3) (solid content: 20%, average particle size: 0.2 μm), 0.08 parts of sulfated cellulose fiber A, 0.12 parts of a shear thinning agent (xanthan gum) [manufactured by Sanjing Co., Ltd., product name: KELZAN], 0.5 parts of a surfactant [manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: PLYSURF AL], 1 part of triethanolamine, 10 parts of diethylene glycol, 5 parts of glycerin and 53.3 parts of water.

[0257] Production of writing tools (Example 1-1)

[0258] The ink composition is sucked and filled into an ink container made of a polypropylene tube, and then connected to a ballpoint pen tip having a superhard ball with a diameter of 0.5 mm at the top through a resin frame. Next, a viscoelastic ink backflow-proof fluid (liquid plug) mainly composed of polybutene is filled from the rear end of the ink container, and a tail plug is further fitted into the rear part of the tube, and a degassing treatment is performed by centrifugation to obtain a ballpoint pen refill.

[0259] Next, the refill is installed in the pen holder to produce a ballpoint pen (retractable ballpoint pen).

[0260] The above-mentioned ballpoint pen has the following structure: the pen tip provided in the ballpoint pen refill is stored in the pen body in a state exposed to the outside air, and the pen tip protrudes from the front end opening of the pen body through the operation of a clip-shaped telescopic mechanism (sliding mechanism) provided on the rear side wall of the pen body.

[0261] Preparation of ink composition (Examples 1-2 to 1-17 and Comparative Examples 1-1 to 1-12)

[0262] The ink compositions of Examples 1-2 to 1-17 and Comparative Examples 1-1 to 1-12 were prepared in the same manner as in Example 1-1, except that the types and amounts of the materials added were changed to those shown in Tables 1 and 2 below.

[0263] Production of Writing Instruments (Examples 1-2 to 1-13 and Comparative Examples 1-1 to 1-9)

[0264] Writing instruments of Examples 1-2 to 1-13 and Comparative Examples 1-1 to 1-9 were produced in the same manner as in Example 1-1.

[0265] Preparation of writing tools (Examples 1-14 to 1-15 and Comparative Example 1-10)

[0266] The ink compositions of Examples 1-14 to 1-15 and Comparative Example 1-10 are impregnated in an ink retaining body formed by coating a polyester strip with a synthetic resin film, contained in a pen body formed of a polypropylene resin, and assembled into a resin-processed pen body (shell-shaped) composed of an extruded body of polyacetal resin having a plurality of ink lead-out holes extending axially connected to the front end of the pen body via a frame, and a pen cap is attached to produce a marking pen (cap-type marking pen).

[0267] Production of Writing Instruments (Examples 1-16 to 1-17 and Comparative Examples 1-11 to 1-12)

[0268] The ink compositions of Examples 1-16 to 1-17 and Comparative Examples 1-11 to 1-12 are impregnated in an ink retaining body formed by covering a polyester strip with a synthetic resin film, contained in a pen body formed of a polypropylene resin, assembled into a resin-processed pen body (chisel-shaped) in which polyester fiber is connected to the front end of the pen body via a resin frame, and a pen cap is attached to produce a marking pen (cap-type marking pen).

[0269] [Table 1]

[0270]

[0271] [Table 2]

[0272]

[0273] The contents of the materials in Tables 1 and 2 are explained according to the marked numbers.

[0274] (1-1) Blue pigment aqueous dispersion (Pigment Blue 15:3) (solid content: 20%, average particle size 0.2 μm).

[0275] (1-2) Black pigment (carbon black) [manufactured by Mitsubishi Chemical Co., Ltd., product name: MA-100 (average particle size: 0.024 μm)].

[0276] (1-3) Reversible thermochromic microcapsule pigment (a pigment that is pre-cooled to below -20°C and develops a blue color).

[0277] (1-4) Plate-like bright pigment (paste-like aluminum powder pigment) [manufactured by TOYO ALUMINIUM CO., LTD., product name: ALPASTE EMERAL EMR-D5660H (solid content: 60%, average particle size: 9 μm)].

[0278] (1-5) Plate-shaped bright pigment (pearlescent pigment) [Merck Japan Co., Ltd., product name: Iriodin 221 (average particle size: 15 μm)].

[0279] (1-6) White pigment (titanium oxide) [produced by TAYCA Corporation, product name: JR-707 (average particle size: 0.25 μm)].

[0280] (1-7) Aqueous dispersion of a peach fluorescent pigment (solid content: 45%, average particle size: 0.4 μm).

[0281] (1-8) Sulfate-esterified fine cellulose fibers having a cellulose type I crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (fiber width: 3 to 6 nm, sulfur introduction amount: 1.47 mmol / g, degree of polymerization: 400 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 4.67%).

[0282] (1-9) Sulfate-esterified fine cellulose fibers having a cellulose type I crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (fiber width: 3 to 6 nm, sulfur introduction amount: 1.57 mmol / g, degree of polymerization: 400 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 1.71%).

[0283] (1-10) Sulfate-esterified fine cellulose fibers having a cellulose type I crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (fiber width: 3 to 6 nm, sulfur introduction amount: 1.81 mmol / g, degree of polymerization: 400 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 0.99%).

[0284] (1-11) Sulfated cellulose fibers having a cellulose I-type crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to form sodium sulfate) (average fiber width: 52 nm, sulfur introduction amount: 2.1 mmol / g, average fiber length: 13 μm).

[0285] (1-12) Sulfated cellulose fibers having a cellulose I type crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (average fiber width: 1 to 6 nm, sulfur introduction amount: 1.72 mmol / g, degree of polymerization: 200 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 1.09%).

[0286] (1-13) Sulfated cellulose fibers having a cellulose type I crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (average fiber width: 1 to 6 nm, amount of sulfur introduced: 2.00 mmol / g, degree of polymerization: 50 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 1.13%).

[0287] (1-14) BYK-Chemie Japan Co., Ltd., product name: DISPER BYK-190 (solid content: 40%).

[0288] (1-15) Manufactured by Sanjing Co., Ltd., product name: KELZAN.

[0289] (1-16) Manufactured by Dow Chemical Japan Co., Ltd., product name: CELLOSIZE WP-09L.

[0290] (1-17) Made by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: PLYSURF AL.

[0291] The fiber width of the sulfated fine cellulose fibers of (1-8) to (1-10) is 3 to 6 nm, and it can be said that the average fiber width is also within the range of 3 to 6 nm.

[0292] It should be noted that the reversible thermochromic microcapsule pigment was prepared as follows.

[0293] A reversible thermochromic composition comprising 3 parts of 3',6'-bis[phenyl(3-methylphenyl)amino]spiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one as component (A), 3 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane and 5 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as components (B), and 50 parts of 4-benzyloxyphenylethyl decanoate as component (C) was added to a mixed solution comprising 35 parts of an aromatic isocyanate prepolymer as a wall material and 40 parts of a cosolvent, and then emulsified and dispersed in an 8% polyvinyl alcohol aqueous solution, and stirred while heating, and then 2.5 parts of a water-soluble aliphatic modified amine was added, and stirring was further continued to prepare a microcapsule dispersion. A reversible thermochromic microcapsule pigment having an average particle size of 1.9 μm was obtained from the microcapsule dispersion by centrifugation.

[0294] The reversible thermochromic microcapsule pigment has a complete color development temperature t1 of -20°C and a complete decolorization temperature t4 of 60°C, and reversibly changes from blue to colorless by temperature change.

[0295] The specific gravity of the reversible thermochromic microcapsule pigment in a fully colored state is 1.08 to 1.09 at 20° C. based on water.

[0296] [Evaluation of initial writing performance]

[0297] Using each writing tool made in Examples 1-1 to 1-17 and Comparative Examples 1-1 to 1-12, write a 15 cm straight line in a direction parallel to the short dimension of A4 size test paper (vertical) at room temperature (20°C) for 5 lines. Here, when using the writing tools made in Examples 1-16 to 1-17 and Comparative Examples 1-11 to 1-12, write with the wide side of the pen body close to the paper surface. It should be noted that the test paper used was writing paper A based on old JIS P3201.

[0298] The handwriting obtained was visually confirmed and evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4 below, and the evaluation "A" was regarded as passing.

[0299] A: There is no flying white or flying lines in the handwriting, and the handwriting has good concentration and line width.

[0300] B: The handwriting has many flying whites and / or flying lines. Or it is impossible to write.

[0301] [Evaluation of writing performance after time]

[0302] Each writing instrument subjected to the writing test was placed in a thermostatic chamber set at 50°C with the pen tip facing downward for 30 days. After 30 days, the writing instruments were taken out of the thermostatic chamber and handwritten in a 15 cm straight line in a direction parallel to the short dimension of the A4-sized test paper (vertical direction) at room temperature (20°C) for 5 lines. Here, when using the writing instruments made in Examples 1-16 to 1-17 and Comparative Examples 1-11 to 1-12, the wide side of the pen body was pressed against the paper surface for writing. It should be noted that the test paper used was writing paper A in accordance with JIS P3201.

[0303] The handwriting obtained was visually confirmed and evaluated according to the following criteria. The evaluation results are shown in Tables 3 and 4 below, and evaluations "A" and "B" were considered acceptable.

[0304] A: There are no flying white spots or flying lines in the handwriting, and the color of the handwriting is the same as or at the same level as the initial handwriting, and good handwriting is obtained.

[0305] B: The handwriting has some loose white spots and / or loose lines, and the color of the handwriting is slightly darker than the initial handwriting, but it is at a level that does not cause any practical problems.

[0306] C: Writing is possible, but the color of the handwriting is darker than the initial handwriting, and the color of the handwriting is different.

[0307] D: The handwriting has many flying whites and / or flying lines. Or it is impossible to write.

[0308] [Table 3]

[0309]

[0310] [Table 4]

[0311]

[0312] [Example 2]

[0313] The following Example 2 shows that the ink composition according to an embodiment of the present invention and the writing instrument containing the ink composition do not drip when the writing instrument is stored for a long period of time with the pen tip facing downward, and can form good handwriting without blurring or the like.

[0314] The compositions of the ink compositions of Examples are shown in Table 5 below, and the compositions of the ink compositions of Comparative Examples are shown in Table 6. The numerical values ​​of the compositions in the tables represent parts by mass.

[0315] [Table 5]

[0316]

[0317] [Table 6]

[0318]

[0319] The contents of the raw materials in the table are described according to the marked numbers.

[0320] (2-1) Red dye (Acid Red 289).

[0321] (2-2) Blue dye (Acid Blue 90).

[0322] (2-3) Yellow dye (Acid Yellow 9).

[0323] (2-4) Black pigment (carbon black) [manufactured by Mitsubishi Chemical Co., Ltd., product name: MA-100 (average particle size: 0.024 μm)].

[0324] (2-5) A thermochromic blue pigment, specifically, a microcapsule pigment (T1: -14°C, T2: -6°C, T3: 48°C, T4: 60°C, ΔH: 64°C, average particle size: 2.3 μm, color changes from blue to colorless) containing a reversible thermochromic composition comprising 2.0 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azophthalide as the component (A), 8.0 parts of 2,2-bis(4'-hydroxyphenyl)hexafluoropropane as the component (B), and 50.0 parts of 4-benzyloxyphenylethyl decanoate as the component (C).

[0325] (2-6) BYK-Chemie Japan Co., Ltd., product name: DISPER BYK-190 (solid content: 40%).

[0326] (2-7) Made by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: PLYSURF AL.

[0327] (2-8) Sulfate-esterified fine cellulose fibers having a cellulose type I crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (fiber width: 3 to 6 nm, sulfur introduction amount: 1.47 mmol / g, degree of polymerization: 400 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 4.67%).

[0328] (2-9) Sulfate-esterified fine cellulose fibers having a cellulose type I crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (fiber width: 3 to 6 nm, sulfur introduction amount: 1.57 mmol / g, degree of polymerization: 400 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 1.71%).

[0329] (2-10) Sulfate-esterified fine cellulose fibers having a cellulose I type crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (fiber width: 3 to 6 nm, sulfur introduction amount: 1.81 mmol / g, degree of polymerization: 400 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 0.99%).

[0330] (2-11) Sulfated cellulose fibers having a cellulose I-type crystal structure, in which a portion of the hydroxyl groups of the cellulose fibers are sulfated (to form sodium sulfate) (average fiber width: 52 nm, sulfur introduction amount: 2.1 mmol / g, average fiber length: 13 μm).

[0331] (2-12) Sulfated cellulose fibers having a cellulose type I crystal structure, wherein a portion of the hydroxyl groups of the cellulose fibers are sulfated (to become sodium sulfate) (average fiber width: 1 to 6 nm, amount of sulfur introduced: 2.00 mmol / g, degree of polymerization: 50 to 600, haze value in an aqueous solution with a solid content concentration of 0.5 mass %: 1.13%).

[0332] (2-13) Manufactured by Sanjing Co., Ltd., product name: KELZAN.

[0333] (2-14) Manufactured by Dow Chemical Japan Co., Ltd., product name: CELLOSIZE WP-09L.

[0334] (2-15) Produced by Asahi Kasei Corporation, trade name: CEOLUS RC-N30 (active ingredient: 1.5%).

[0335] (2-16) Manufactured by Mitsui Chemicals, Inc., trade name: CHEMIPEARL W900 (active ingredient: 40%).

[0336] (2-17) Manufactured by Mitsui Chemicals, Inc., trade name: CHEMIPEARL W401 (active ingredient: 40%).

[0337] (2-18) Manufactured by BASF, trade name: Sokalan K90.

[0338] The fiber width of the sulfated fine cellulose fibers of (2-8) to (2-10) is 3 to 6 nm, and it can be said that the average fiber width is also within the range of 3 to 6 nm.

[0339] Preparation of ink (Examples 2-1 to 2-13 and Comparative Examples 2-1 to 2-10)

[0340] The raw materials not including the shear-thinning agent in the formulation of each embodiment and comparative example were mixed and stirred at 1000 rpm for 1 hour at 20° C. using a disperser. For the example containing the shear-thinning agent, the shear-thinning agent was added to the mixed solution of the raw materials not including the shear-thinning agent and further stirred for 1 hour to obtain a ballpoint pen ink composition. It should be noted that the shear-thinning agent was used in the state of a pre-carrier prepared by pre-dispersing it in water.

[0341] Production of Writing Instruments (Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-8)

[0342] The ballpoint pen refill includes: a conical cutting ballpoint pen tip (accommodating a ball push spring that pushes the ball forward) that rotatably holds the ball at the front end; a connecting member fixed to the ballpoint pen tip at the front; an ink containing tube fixed to the front end opening and containing ink and an ink-proof reverse fluid; and a tail plug fixed to the rear end opening of the ink containing tube. It should be noted that the ink-proof reverse fluid is an ink-proof reverse fluid that is kneaded using polybutene as a base oil and fatty acid amide as a thickener.

[0343] It should be noted that the ball with a diameter of 0.5 mm is used in the ballpoint pen refill.

[0344] The sample ballpoint pen was obtained by accommodating each ballpoint pen refill in a state of biasing from the rear by a spring (coil spring) inside a pen barrel having a clip on the rear outer surface. The ballpoint pen is a retractable type in which the ballpoint pen tip protrudes from the front end hole of the pen barrel by pressing the rear end (push operation part) of the pen barrel forward.

[0345] Production of Writing Instruments (Examples 2-11 to 2-13 and Comparative Examples 2-9 to 2-10)

[0346] The above-mentioned ink composition is impregnated in an ink storage body formed by covering a polyester strip with a synthetic resin film, contained in a pen body formed of a polypropylene resin, and assembled into a resin-processed pen body (shell-shaped) composed of an extruded body of polyacetal resin having a plurality of ink outlet holes extending in the axial direction connected to the front end of the pen body via a frame, and a pen cap is attached to produce a marking pen (cap-type marking pen).

[0347] The following tests were carried out using a ballpoint pen and a marker pen for each sample.

[0348] Drop test

[0349] Each writing instrument was used so that the pen tip was exposed from the pen holder and held facing downward. After being left in an atmosphere of temperature 20°C / relative humidity 95% or temperature 30°C / relative humidity 80% for 20 hours, the appearance of the tip of the pen tip was visually observed.

[0350] Writing test

[0351] Each writing instrument confirmed to be able to write was left standing in a horizontal position for 24 hours in an atmosphere of temperature 20°C and relative humidity 60% with the pen tip exposed from the pen barrel, and then a straight line was handwritten on JIS P3201 writing paper A, and the state of the handwriting was visually observed.

[0352] The test results are shown in Table 7 below.

[0353] [Table 7]

[0354]

[0355] In addition, the contents of the evaluation symbols of the test results are as follows.

[0356] Drip test (Evaluation "A" and "B" are considered pass.)

[0357] A: No dripping of ink was observed.

[0358] B: Ink seeps out from the front end of the pen tip.

[0359] C: Ink drops are confirmed at the tip of the pen.

[0360] Writing test (evaluation "0" is considered as pass.)

[0361] ○: Handwriting with a certain density and line width is stably obtained.

[0362] ×: The handwriting produces flying white.

[0363] This application claims the priority of two Japanese patent applications, Japanese Patent Application No. 2022-133582 and Japanese Patent Application No. 2022-133588, both filed on August 24, 2022. Japanese Patent Application No. 2022-133582 and Japanese Patent Application No. 2022-133588 are incorporated into this specification by reference.

Claims

1. A water-based ink composition for writing instruments, wherein: The invention comprises water, a colorant, and sulfated cellulose fibers in which at least a part of the hydroxyl groups of the cellulose fibers are sulfated.

2. The aqueous ink composition for writing instruments according to claim 1, wherein The sulfated cellulose fibers have a cellulose I-type crystal structure, and at least a portion of hydrogen atoms of hydroxyl groups of the cellulose fibers are substituted with sulfonic groups represented by the following formula (1): <h2 style=";text-align:left;direction:ltr">(-SO3<h2 style=";text-align:left;direction:ltr"> － <h2 style=";text-align:left;direction:ltr"> )<h2 style=";text-align:left;direction:ltr"> r <h2 style=";text-align:left;direction:ltr"> ·Z<h2 style=";text-align:left;direction:ltr"> r+ <h2 style=";text-align:left;direction:ltr"> ……(1) Where r is a natural number from 1 to 3. When r = 1, Z r+ is at least one selected from the group consisting of hydrogen ions, alkali metal cations, ammonium ions, aliphatic ammonium ions, and aromatic ammonium ions. In addition, when r=2 or 3, Z r+ It is at least one selected from the group consisting of alkaline earth metal cations and polyvalent metal cations.

3. The aqueous ink composition for writing instruments according to claim 1 or 2, wherein The average fiber width of the sulfated cellulose fibers is 0.5 to 500 nm.

4. The aqueous ink composition for writing instruments according to claim 3, wherein The average fiber width of the sulfated cellulose fibers is 30 nm or less.

5. The aqueous ink composition for writing instruments according to any one of claims 1 to 4, wherein The amount of sulfur introduced into the sulfated cellulose fibers is higher than 0.42 mmol / g.

6. The aqueous ink composition for writing instruments according to any one of claims 1 to 5, wherein The degree of polymerization of the sulfated cellulose fibers is 30 or more.

7. The aqueous ink composition for writing instruments according to any one of claims 1 to 6, wherein The haze value of a dispersion obtained by dispersing the sulfated cellulose fibers in a water-soluble solvent so as to have a solid content concentration of 0.5% by mass is 20% or less.

8. The aqueous ink composition for writing instruments according to any one of claims 1 to 7, wherein The sulfated cellulose fibers are blended in an amount within a range of 0.01 to 3% by mass in the total amount of the ink composition.

9. The aqueous ink composition for writing instruments according to any one of claims 1 to 8, wherein A shear-thinning agent is also included.

10. The aqueous ink composition for writing instruments according to claim 9, wherein The shear-thinning agent is selected from the group consisting of water-soluble polysaccharides, polymers with a molecular weight of 100,000 to 150,000 with alkyl esters of methacrylic acid as the main component, poly-N-vinyl carboxylic acid amide crosslinked products, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali thickening type acrylic resin, crosslinked acrylic polymer, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, and metal salts or amine salts of dialkyl sulfosuccinic acid.

11. The aqueous ink composition for writing instruments according to claim 9 or 10, wherein The shear-thinning agent is blended in an amount within a range of 0.05 to 1% by mass based on the total amount of the ink composition.

12. The aqueous ink composition for writing instruments according to any one of claims 1 to 11, wherein The colorant is dispersed in water.

13. The aqueous ink composition for writing instruments according to any one of claims 1 to 12, wherein The colorant includes at least one selected from the group consisting of pigments and resin particles.

14. The aqueous ink composition for writing instruments according to any one of claims 1 to 13, wherein The average particle size of the colorant is 0.01 to 25 μm.

15. The aqueous ink composition for writing instruments according to any one of claims 1 to 14, wherein Contains coloring agent having a specific gravity greater than 1.

16. A writing instrument, wherein: The aqueous ink composition for writing instruments according to any one of claims 1 to 15 is contained.

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