Water-based ink composition for writing instruments and writing instrument

Abstract

Provided are a water-based ink composition for writing instruments and a writing instrument that exhibit excellent pigment anti-settling properties, ink followability, and color development on paper, and that achieve low gloss of drawn lines.　The water-based ink composition for writing instruments according to the present disclosure is characterized by containing at least a colorant, a neutralized product (A) of an isobutylene-maleic anhydride copolymer, a fibrous polysaccharide (B), and water, wherein the mass ratio (A) / (B) of the neutralized product (A) of the isobutylene-maleic anhydride copolymer to the fibrous polysaccharide (B) is 0.5 to 20.

Description

Water-based ink composition for writing instruments and writing instruments 【0001】 This specification relates to a water-based ink composition for writing instruments and writing instruments. 【0002】 Conventionally, when imparting "concealability" that is less affected by the color of the background, water-based ink compositions for writing instruments that use high-specific gravity pigments such as titanium oxide in the coloring material are widely known. However, pigments with a high specific gravity and large particle size such as titanium oxide are likely to settle, and cases where the ink viscosity is increased to solve this problem are known. 【0003】 When the ink viscosity is increased, the ink followability deteriorates during rapid writing, and streaks may occur, resulting in insufficient concealability. Also, when the particle size of the pigment is reduced as a means of suppressing sedimentation, the ink viscosity can be lowered to some extent, but there is a problem that it easily enters the mesh of paper fibers, and as a result, sufficient concealability cannot be obtained. These points were exemplified with titanium oxide, but it is known that the same problems occur not only with titanium oxide but also when using high-specific gravity pigments such as glitter pigments like metallic flakes. 【0004】On the other hand, conventional aqueous ink compositions suitable for writing instruments, etc., that have good pigment settling properties and ink followability, and technologies adjacent to the present invention include, for example, (1) an aqueous ink composition for marking pens that, even when an aqueous ink using a pigment as a coloring agent is applied to a marking pen, can maintain a stable dispersion state in the ink over a long period of time and continuously exhibit good writing performance without causing smudging or other issues in the writing, comprising water, pigment, fermented cellulose, and a crosslinking agent that crosslinks the pigment and fermented cellulose (see, for example, Patent Document 1), (2) an aqueous ink composition for writing instruments that has excellent dispersion stability and can suppress smudging and skipping of lines and form good writing, comprising a microcapsule pigment consisting of a core material and a wall film enclosing the core material, a polyether phosphate ester as a dispersant, cellulose nanofiber, and water (see, for example, Patent Document 2), (3) (4) A water-soluble ink composition for writing instruments is known that comprises at least a colorant, a neutralized product of an isobutylene-maleic anhydride copolymer, a water-soluble resin and / or a resin emulsion, and water, wherein the acid value of the resin in the water-soluble resin and resin emulsion is 240 or less (see, for example, Patent Document 3), (5) a water-soluble ink composition for writing instruments is known that comprises at least a colorant, a neutralized product of an isobutylene-maleic anhydride copolymer, a polyol having two or more OH groups, a water-soluble resin and / or a resin emulsion, and water (see, for example, Patent Document 4). 【0005】However, the aqueous ink compositions for writing instruments using fermented cellulose or cellulose nanofibers described in Patent Documents 1 and 2 above are sometimes affected by the underlying color when writing on black paper, resulting in insufficient color development on the paper surface. Furthermore, they have poor resistance to pigment sedimentation, and there are still issues with ink followability when writing quickly. The aqueous ink compositions for writing instruments described in Patent Documents 3 and 4 above are similar to the present invention in that they use a neutralized product of isobutylene-maleic anhydride copolymer, but they provide an aqueous ink composition for writing instruments that forms a uniform coating film and has excellent abrasion resistance and water adhesion resistance even when writing on non-absorbent surfaces. Therefore, they differ from the present invention in terms of the purpose and problems of the invention, as well as the technical concept (composition and its effects). 【0006】 Japanese Patent Publication No. 2015-10114 (Claims, Examples, etc.) Japanese Patent Publication No. 2024-76078 (Claims, Examples, etc.) Japanese Patent Publication No. 2023-78817 (Claims, Examples, etc.) Japanese Patent Publication No. 2023-92768 (Claims, Examples, etc.) 【0007】 This disclosure aims to address the problems and current state of the above-mentioned prior art, and to provide an aqueous ink composition and writing instrument for writing instruments that can produce highly colored lines without being affected by the color of the background when writing on black paper, and that can highly simultaneously achieve the following characteristics: 1) resistance to pigment sedimentation, 2) ink followability when writing quickly, 3) color development on the paper surface, and 4) low gloss of the lines. 【0008】 In view of the above-mentioned conventional problems, the Disclosers conducted intensive research and found that by containing at least a colorant, a neutralized product of isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and water, and by setting the mass ratio (A) / (B) of the neutralized product of isobutylene-maleic anhydride copolymer (A) to the fibrous polysaccharide (B) within a specific range, an aqueous ink composition for writing instruments and a writing instrument for the above-mentioned purpose can be obtained, and thus completed this disclosure. 【0009】In other words, the aqueous ink composition for writing instruments of this disclosure contains at least a colorant, a neutralized product of isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and water, and is characterized in that the mass ratio (A) / (B) of the neutralized product of isobutylene-maleic anhydride copolymer (A) to the fibrous polysaccharide (B) is 0.5 to 20. The aqueous ink composition for writing instruments further preferably contains 0.03 to 2% by mass of an anionic or nonionic surfactant. The viscosity of the ink of the aqueous ink composition for writing instruments is such that the viscosity neutralized product of isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and water, and the mass ratio (A) / (B) is such that the viscosity is such that the ratio is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is such that the viscosity is －１ In this case, the pressure is preferably 10 to 550 mPa·s. The writing instrument of this disclosure is characterized by being equipped with the aqueous ink composition for writing instruments having the above configuration. 【0010】 This disclosure provides an aqueous ink composition and writing instrument for writing instruments that, when written on black paper or the like, produces highly colored lines without being affected by the underlying color, exhibits excellent resistance to pigment sedimentation, ink followability when writing quickly, and color development on the paper surface, resulting in low gloss lines. The purposes and effects of this disclosure are recognized and obtained by using the components and combinations indicated in the claims in particular. Both the general description above and the detailed description below are illustrative and descriptive and do not limit the disclosure as described in the claims. 【0011】 The embodiments of this disclosure are described in detail below. However, it should be noted that the technical scope of this disclosure is not limited to the embodiments described below, but extends to the inventions described in the claims and their equivalents. Furthermore, this disclosure can be implemented based on the contents disclosed herein and common technical knowledge in the art (including design matters and obvious matters). 【0012】 <Aqueous Ink Composition for Writing Instruments> The aqueous ink composition for writing instruments of the present disclosure contains at least a colorant, a neutralized product of isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and water, and is characterized in that the mass ratio (A) / (B) of the neutralized product of isobutylene-maleic anhydride copolymer (A) to the fibrous polysaccharide (B) is 0.5 to 20. 【0013】<Colorants> The colorants used in this disclosure include conventionally known inorganic and organic pigments such as titanium dioxide, resin particle pigments containing pigments, pseudo-pigments obtained by coloring resin emulsions with dyes, thermochromic pigments, photochromic particles and other colored resin particle pigments, white plastic pigments, pigments with silica or mica as a base material and multi-layer coating of iron oxide or titanium dioxide on the surface, foil-like pigments (glitter pigments) obtained by cutting luminous films or foils, luminous pigments such as aluminum pigments, and all dyes that are soluble or dispersed in water, without limitation. 【0014】Examples of inorganic pigments that can be used include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. More specifically, inorganic pigments such as carbon black, titanium black, zinc oxide, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, lead yellow, molybdide orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, navy blue, navy blue, manganese violet, aluminum powder, brass powder, etc., C.I. Pigment Blue 17, C.I. Pigment Blue 3-15, C.I. Pigment Blue 17, C.I. Pigment Blue 27, C.I. Pigment Red 5, C.I. Pigment Red 22, C.I. Pigment Red 38, C.I. Pigment Red 48, C.I. Pigment Red 49, C.I. Pigment Red 53, C.I. Pigment Red 57, C.I. Pigment Red 81, C.I. Pigment Red 104, C.I. Pigment Red 146, C.I. Pigment Red 245, C.I. Pigment Yellow 1, C.I. Pigment Yellow 3, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 17, C.I. Pigment Yellow 34, C.I. Pigment Yellow 55, C. Examples include I. Pigment Yellow 74, C. I. Pigment Yellow 95, C. I. Pigment Yellow 166, C. I. Pigment Yellow 167, C. I. Pigment Orange 5, C. I. Pigment Orange 13, C. I. Pigment Orange 16, C. I. Pigment Violet 1, C. I. Pigment Violet 3, C. I. Pigment Violet 19, C. I. Pigment Violet 23, C. I. Pigment Violet 50, C. I. Pigment Green 7, etc. 【0015】Examples of dyes include acid dyes such as eosin, foxine, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and negrosine NB; direct dyes such as direct black 154, direct sky blue 5B, and violet BB; and basic dyes such as rhodamine and methyl violet. 【0016】 These colorants can be used individually or in mixtures of two or more (hereinafter referred to as "at least one"). Furthermore, from the viewpoint of color development and weather resistance, it is preferable to use all pigments, or to use pigments as the main component with dyes as complementary colors (50% to 100% by mass of pigment in the total amount of colorant). The pigments should preferably be water-dispersible pigments, resin particle pigments, pseudo-pigments, white plastic pigments, multi-layer coated pigments, glitter pigments, aluminum pigments, thermochromic pigments, or light-chromic particles. The average particle size of these pigments varies depending on the type of writing instrument (ballpoint pen, marking pen, etc.), ink composition, viscosity, etc., but from the viewpoint of color development on paper and resistance to pigment sedimentation, an average particle size of 0.05 to 20 μm is desirable. The content of these colorants can be appropriately increased or decreased according to the ink line density, and is preferably 0.1 to 30% by mass (hereinafter, "mass%" is simply referred to as "%") relative to the total amount of the ink composition. 【0017】 In this disclosure, "average particle diameter" refers to the D-50 value measured with a laser diffraction / scattering particle diameter analyzer (model: LA-960, Horiba, Ltd.). The shape of the colorant incorporated into the ink composition of this disclosure may be spherical or non-spherical. 【0018】The neutralized isobutylene-maleic anhydride copolymer (A) used in this disclosure is a neutralized copolymer of isobutylene and maleic anhydride, and in the ink composition, it creates loose aggregation with the pigment, thereby suppressing the sedimentation of the pigment. In this disclosure, the effects of this disclosure are further enhanced by using it in combination with a fibrous polysaccharide (B) described later, and within a predetermined mass ratio range. The basic structure of the isobutylene-maleic anhydride copolymer used is shown by the following formula (I), and the following formula (II) is an ammonia neutralized (modified) isobutylene-maleic anhydride copolymer that can be preferably used in this disclosure. 【0019】 【0020】 【0021】 In this disclosure, in addition to the ammonia neutralized product of formula (II) above, sodium hydroxide neutralized product and amine neutralized product may also be used. Furthermore, the values ​​of n in formula (I), l and m in formula (II), and j and k in formula (III) below will vary depending on the weight-average molecular weight described later, and a suitable range will be determined. In addition, in this disclosure, the isobutylene-maleic anhydride copolymer represented by formula (III) below, obtained by imidizing (imide-modifying) the isobutylene-maleic anhydride copolymer, may also be neutralized products obtained by neutralizing the imidized isobutylene-maleic anhydride copolymer represented by formula (III) below with ammonia, sodium hydroxide, amine, etc. 【0022】The weight-average molecular weight of each neutralized product obtained by neutralizing the isobutylene-maleic anhydride copolymers of formulas (II) and (III) above is preferably 3,000 to 400,000, more preferably 5,000 to 200,000, even more preferably 30,000 to 100,000, and particularly preferably 50,000 to 70,000. This weight-average molecular weight is the polystyrene equivalent value obtained by aqueous gel permeation chromatography (GPC) analysis. Commercially available products can be used for the isobutylene-maleic anhydride copolymers and their neutralized products. For example, "Isoban" manufactured by Kuraray Co., Ltd. can be used. For example, Isoban-104 and 110 are commercially available ammonia neutralized (modified) products of the isobutylene-maleic anhydride copolymer in formula (II) above. Furthermore, when preparing the neutralized product of the isobutylene-maleic anhydride copolymer used (from formula (I) above, etc.), for example, if all carboxyl groups of the isobutylene-maleic anhydride copolymer are neutralized, the degree of neutralization is considered to be 1, and the necessary amounts of ammonia, sodium hydroxide, amine, etc. used for neutralization are calculated and prepared to obtain each neutralized product. 【0023】 The content of these neutralized isobutylene-maleic anhydride copolymers (A) is preferably 0.01 to 10% by mass, and more preferably 0.05 to 5% by mass, in terms of solid content, relative to the total amount of the ink composition. If the content of these neutralized isobutylene-maleic anhydride copolymers (A) is less than 0.01% by mass, the effects of this disclosure cannot be achieved. On the other hand, if it exceeds 10% by mass, the viscosity increases, reducing the ink discharge performance and potentially adversely affecting writing performance. 【0024】Examples of fibrous polysaccharides (B) used in this disclosure include at least one of fermented cellulose, cellulose nanofibers, chitin, and chitosan. Preferably, due to their low impurity content, fermented cellulose and cellulose nanofibers are preferred. While there are various non-fibrous polysaccharides such as xanthan gum and carboxymethylcellulose (CMC), using these alone will not produce the effects of this disclosure. However, as long as the ink composition contains fibrous polysaccharides as an essential component, xanthan gum, CMC, etc., can be used as appropriate, within the limits that do not impair the effects of this disclosure. In this disclosure, "fibrous" means insoluble in water and having an aspect ratio of 25 or more. 【0025】 The fermented cellulose that can be used is cellulose produced by cellulose-producing bacteria, such as bacteria belonging to the genera Acetobacter, Pseudomonas, Agrobacterium, etc., and is not particularly limited to these types of cellulose. Typically, fermented cellulose can be produced by culturing cellulose-producing bacteria according to known methods (culture medium and conditions, etc.) and purifying the resulting fermented cellulose as desired. Such fermented cellulose has a much finer fiber diameter compared to the fiber diameter of general cellulose fibers derived from plants. Furthermore, the chemical structure of the polysaccharides constituting fermented cellulose is basically a linear high-molecular-weight polysaccharide composed of β1-4 linked glucose molecules. 【0026】 The fermented cellulose that can be used is insoluble in water and forms a three-dimensional network structure in the ink composition. Unlike thickening polysaccharides such as xanthan gum, fermented cellulose has low viscosity and is less sticky, and can be used stably in various inks with different coexisting components, temperatures, and pH levels. Examples of fermented cellulose that can be used include the fermented cellulose obtained in the above production process, as well as commercially available SunArtist series from San-Ei Gen F.F.I., such as SunArtist H-PN and SunArtist H-PG, CELLULON R-27 from CP Kelco, and Fibnano HE-NFBC from Kusano Sakko Co., Ltd. 【0027】The cellulose nanofibers that can be used (hereinafter sometimes referred to as "CNF") are materials obtained by defibrating pulp to a fiber width of 3 to 4 nm by treating it with a phosphate ester or the like. The average fiber length (number-average fiber length) of the cellulose nanofibers that can be used is not particularly limited, but is preferably 100 to 1000 nm, more preferably 150 to 800 nm. The aspect ratio of the cellulose nanofibers (i.e., the ratio of the average fiber length to the average fiber diameter) is preferably in the range of 25 to 250, and even more preferably 35 to 200. Examples of cellulose nanofibers that can be used include TEMPO-oxidized cellulose nanofibers, and commercially available products such as Rheocrysta C-2SP (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content 2%) and Selenpia TC-02X (manufactured by Nippon Paper Industries Co., Ltd., solid content 5%) can be used. The above-mentioned TEMPO-oxidized cellulose nanofibers can be obtained by reacting wood fibers with a TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) catalyst to convert the primary hydroxyl groups of cellulose into carboxyl groups, and then mechanically defibrillating them. 【0028】 The total content of these fibrous polysaccharides (B) is preferably 0.03 to 2.0% by mass, and more preferably 0.05 to 1.0% by mass, in terms of active ingredient amount, relative to the total amount of the ink composition. In this disclosure, it is necessary to set the mass ratio (A) / (B) of the neutralized isobutylene-maleic anhydride copolymer (A) to the fibrous polysaccharides (B) to 0.5 to 20, and more preferably 2.0 to 15. In this disclosure, it is presumed that by setting the mass ratio (A) / (B) to 0.5 to 20, the neutralized product (A) creates loose aggregation, which is then captured by the network of fibrous polysaccharides (B), thereby achieving the effects of this disclosure. If the mass ratio (A) / (B) is less than 0.5, loose aggregation cannot be formed, the pigment slips through the fibrous polysaccharides, reducing its resistance to pigment sedimentation, and even on the paper surface, it penetrates the paper fibers, reducing its color development and preventing the effects of the present disclosure from being achieved. On the other hand, if the mass ratio (A) / (B) exceeds 20, the pigment cannot be supported by loose aggregation, resulting in reduced resistance to pigment sedimentation, which is undesirable. 【0029】 In this disclosure, it is desirable to further include at least one anionic or nonionic surfactant in order to maintain the effects of this disclosure to an even higher degree. Examples of nonionic surfactants that can be used include polyoxyalkylene higher fatty acid esters, higher fatty acid partial esters of polyhydric alcohols, higher fatty acid esters of sugars, monophosphate esters of polyoxyethylene alkyl ethers or polyoxyethylene alkylaryl ethers, diphosphate esters of polyoxyethylene alkyl ethers or polyoxyethylene alkylaryl ethers, triesters of polyoxyethylene alkyl ethers or polyoxyethylene alkylaryl ethers, alkyl phosphate esters, alkyl ether phosphate esters, or derivatives thereof. Specifically, examples include glycerin fatty acid esters, polyglycerin fatty acid esters, propylene glycol fatty acid esters, pentaerythritol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene phytosterols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene styrene-derived phenyl ethers, polyoxyethylene disstyrene-derived phenyl ethers, polyoxyethylene hydrogenated castor oil, polyoxyethylene lanolin, polyoxyethylene lanolin alcohol, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, and polyoxyethylene alkylphenyl formaldehyde condensates. 【0030】Furthermore, examples of anionic surfactants that can be used include alkylated sulfonates of higher fatty acid amides, alkylallyl sulfonates, naphthalene sulfonic acid formaldehyde condensates, and more specifically, alkyl sulfates, polyoxyethylene alkyl ether sulfates, N-acyl amino acid salts, N-acyl methyl taurate salts, polyoxyethylene alkyl ether acetates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, and polycarboxylates. The nonionic surfactants described above are preferably monophosphate esters of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, diphosphate esters of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, triesters of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, alkyl phosphate esters, alkyl ether phosphate esters or derivatives thereof, polyoxyethylene distyrenated phenyl ether, polyoxyethylene polyoxypropylene copolymer, and polyoxyethylene fatty acid ester. Commercially available phosphate esters include Phosphanol RD-510Y, RB-410, and RS-610 from the Phosphanol series (manufactured by Toho Chemical Industry Co., Ltd.). Commercially available polyoxyethylene distyrenated phenyl ethers include Neugen EA-177 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Among the anionic surfactants described above, commercially available lauryl sulfates include Emal 2FG manufactured by Kao Corporation. 【0031】 The content of these anionic or nonionic surfactants is preferably 0.03 to 2% by mass, and more preferably 0.2 to 1.0% by mass, relative to the total amount of the ink composition, in order to further moderately mitigate the mild aggregation caused by the neutralized product to achieve suitable mild aggregation and to maintain the effects of the present disclosure to an even higher degree. By setting the content of these surfactants to 0.03% by mass or more, the effects of the present disclosure can be further exhibited, while by setting it to 2% by mass or less, the effects of the present disclosure can be maintained to an even higher degree. 【0032】The aqueous ink composition for writing instruments disclosed herein contains at least the above-mentioned colorant, a neutralized product of isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and the remainder being water as a solvent (tap water, purified water, distilled water, deionized water, pure water, etc.), with a mass ratio (A) / (B) of the neutralized product of isobutylene-maleic anhydride copolymer (A) to the fibrous polysaccharide (B) being 0.5 to 20. Other components that do not impair the effects of the disclosed herein may appropriately include dispersants, lubricants, pH adjusters, rust inhibitors, preservatives or antibacterial agents, thickeners, etc. 【0033】 Examples of dispersants that can be used include resin compounds such as styrene-acrylic acid copolymers and styrene-maleic acid copolymers, as well as surfactants such as polyoxyethylene alkyl ethers and sodium alkylbenzene sulfonate. Examples of lubricants include nonionic compounds such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphate esters, which are also used as surface treatment agents for pigments; anionic compounds such as alkyl sulfonates and alkylallyl sulfonates of higher fatty acid amides; derivatives of polyalkylene glycols; fluorinated surfactants; and polyether-modified silicones. 【0034】 Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonic acid and phosphoric acid such as sodium tripolyphosphate and sodium carbonate, and alkali metal hydrates such as sodium hydroxide. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitride, and saponins, while examples of preservatives or antibacterial agents include phenol, sodium omazine, sodium benzoate, and benzimidazole compounds. 【0035】The aqueous ink composition for writing instruments disclosed herein contains at least a colorant, a neutralized isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and water. The other components are appropriately combined according to the application of the ink for writing instruments (ballpoint pens, marking pens, etc.), and the mass ratio (A) / (B) is adjusted to be within a predetermined range. The mixture is then stirred and mixed using a stirrer such as a homomixer, homogenizer, or disper. If necessary, coarse particles in the ink composition are removed by filtration or centrifugation to obtain the aqueous ink composition for writing instruments disclosed herein. Furthermore, the pH (25°C) of the aqueous ink composition for writing instruments disclosed herein is preferably adjusted to 5 to 10 using a pH adjuster, and more preferably to 6 to 9.5, from the viewpoint of usability, safety, stability of the ink itself, and compatibility with the ink container. 【0036】 Furthermore, the aqueous ink composition for writing instruments disclosed herein has a viscosity at 25°C that is equal to a shear rate of 38.3 s, in order to further improve resistance to pigment sedimentation and fast writing followability, and to maintain color development and low gloss on the paper surface. －１ In this case, the viscosity is preferably 10 to 550 mPa·s. The viscosity of the ink can be adjusted by suitably combining the amounts of the neutralized substance (A), fibrous polysaccharide (B), water, and other blending components, the blending method (ink preparation), and the dispersion machine. 【0037】The aqueous ink composition for writing instruments of this disclosure, configured in this manner, contains at least a colorant, a neutralized product of isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and water. By setting the mass ratio (A) / (B) of the neutralized product of isobutylene-maleic anhydride copolymer (A) to the fibrous polysaccharide (B) to 0.5 to 20, the colorant, which is appropriately aggregated by the neutralized product of isobutylene-maleic anhydride copolymer (A), rides on the network of fibrous polysaccharide (B). This results in a highly pigmented line that is unaffected by the underlying color when writing on black paper, and provides an aqueous ink composition for writing instruments that highly balances the following characteristics: 1) resistance to pigment sedimentation, 2) ink followability when writing quickly, 3) color development on the paper surface, and 4) low gloss of the line. Furthermore, including anionic surfactants such as alkyl sulfates or nonionic surfactants such as phosphate esters allows for even more appropriate control of the degree of aggregation, thus enabling the further effects of this disclosure when added. 【0038】 <Writing Instruments> The writing instruments of this disclosure are characterized by being equipped with the above-described aqueous ink composition for writing instruments. Examples of writing instruments include ballpoint pens, marking pens, felt pens, etc., equipped with pen tip parts such as ballpoint pen tips, fiber tips, felt tips, plastic tips, fiber cores, and porous cores. 【0039】In this disclosure, "marking pen" means a pen having a mechanism for supplying ink stored in an ink reservoir to a resin writing section by capillary action, and also includes pens referred to as "sign pens." Furthermore, "ballpoint pen" means a pen having a mechanism for releasing ink stored in an ink reservoir by the rotation of a ball provided in the writing section. As a ballpoint pen, the aqueous ink composition for writing instruments having the above composition is contained in an ink reservoir (refill) for ballpoint pens equipped with a ball with a diameter of 0.18 to 2.0 mm, and an ink follower is added. The ink follower is a liquid that is incompatible with the aqueous ink composition for writing instruments having the above characteristics contained in the ink reservoir and has a lower specific gravity than the aqueous ink composition, such as polybutene, silicone oil, or mineral oil. The structure of ballpoint pens, marking pens, etc., is not particularly limited. For example, a direct-ink type ballpoint pen or marking pen may have a collector structure (ink holding mechanism) in which the barrel itself serves as the ink reservoir and the aqueous ink composition for writing instruments with the above configuration is filled into the barrel. In the above, the viscosity of the ink at 25°C is given by a shear rate of 38.3 s. －１ In this case, a preferred range is 10 to 550 mPa·s, and the viscosity range of the aqueous ink composition for writing instruments of this disclosure can be set to an even more preferred range depending on the type of writing instrument (ballpoint pen, marking pen, etc.). For ballpoint pens, a range of 30 to 550 mPa·s is preferred, and for marking pens (including felt-tip pens), a range of 10 to 70 mPa·s is preferred in that a good writing flow rate can be obtained. 【0040】 In a writing instrument configured in this way, a water-based ink composition for writing instruments with the above-mentioned characteristics will be used, resulting in a writing instrument (ballpoint pen, marking pen, felt-tip pen, etc.) that can produce highly vibrant lines without being affected by the underlying color when writing on black paper, and that can achieve a high degree of balance between 1) resistance to pigment settling, 2) ink followability when writing quickly, 3) color development on the paper surface, and 4) low gloss lines. 【0041】Next, the present disclosure will be described in more detail with reference to Examples and Comparative Examples, but the present disclosure is not limited to the following Examples and the like. 【0042】 〔Examples 1 to 24 and Comparative Examples 1 to 10〕A writing instrument aqueous ink composition for ballpoint pens was prepared by a conventional method according to the formulation shown in Table 1 below. Also, a writing instrument aqueous ink composition for marking pens was prepared by a conventional method according to the formulation shown in Table 2 below. When the pH of each writing instrument aqueous ink composition for ballpoint pens and marking pens at room temperature (25°C) was measured with a pH meter (manufactured by HORIBA), it was within the range of 7.9 to 8.2. For each of the writing instrument (for ballpoint pens and marking pens) aqueous ink compositions obtained above, the viscosity value at a shear rate of 38.3 / s at 25°C was measured by the following method. Also, writing instruments (aqueous ballpoint pens and marking pens) were manufactured by the following method, and the evaluation of pigment sedimentation resistance, quick writing followability, color development on paper, and low glossiness of the drawn line was carried out by the following evaluation methods. These results are shown in Table 1 and Table 2 below. 【0043】 (Method for measuring viscosity) The viscosity value at a shear rate of 38.3 / s at 25°C was measured with an EMD viscometer (manufactured by Tokyo Keiki Co., Ltd.). 【0044】 (Manufacture of aqueous ballpoint pens) Aqueous ballpoint pens were manufactured using each of the ink compositions obtained above. Specifically, using the shaft of a ballpoint pen [manufactured by Mitsubishi Pencil Co., Ltd., trade name: Signo UM-100], an ink storage tube made of polypropylene with an inner diameter of 4.0 mm and a length of 113 mm, a stainless steel tip (tungsten carbide ball, ball diameter 0.5 mm), and a refill consisting of a joint connecting the storage tube and the tip were filled with the aqueous ink compositions of Examples 1 to 12 and Comparative Examples 1 to 5 obtained above, and an ink follower mainly composed of mineral oil was loaded at the rear end of the ink to manufacture an aqueous ballpoint pen. 【0045】(Production of Marker Pens) Marker pens were produced using each of the ink compositions obtained above. Specifically, marker pens [manufactured by Mitsubishi Pencil Co., Ltd., trade name: PC-5M, shaft material: recycled PP resin, pen core: PET fiber core] were filled with the aqueous ink compositions of Examples 13 to 24 and Comparative Examples 6 to 10 obtained above to produce marker pens. 【0046】 (Evaluation Method for Pigment Sedimentation Resistance) Each of the ink compositions obtained above was set in a test tube and centrifuged at 5000 rpm for 10 minutes. Then, the ink in the test tube was divided into upper and lower parts, developed, and evaluated according to the following evaluation criteria. Evaluation Criteria: A: There is no difference in density between the upper and lower parts at all. B: When developed side by side, there is a slight difference, but it is hardly noticeable. C: There is a difference between the upper and lower parts, with the upper part being light and the lower part being dark. 【0047】 (Evaluation Method for Quick Writing Followability) Using the above aqueous ballpoint pens and marker pens, freehand writing was performed on writing paper conforming to the ISO standard at 3 times the speed, 2 times the speed, and normal speed respectively, and each written line was evaluated according to the following evaluation criteria. Evaluation Criteria: A: There is no smudging even when writing at 3 times the speed, and writing can be performed smoothly and stably. B: There is no smudging during writing at normal speed and 2 times the speed, and writing can be performed smoothly and stably. C: Even when writing normally, the ink does not follow and line breaks occur. 【0048】 (Evaluation Method for Color Development) After writing a 5-turn spiral on black paper using the above aqueous ballpoint pens and marker pens, the color development of the written line was visually evaluated based on the following evaluation criteria. Evaluation Criteria: A: Very dark and vivid without being affected by the color of the background. B: Dark without being affected by the color of the background. C: Affected by the color of the background and light. 【0049】(Method for evaluating the low gloss of the drawn lines) Using the above-mentioned water-based ballpoint pen and marking pen, a 10 mm square colored film was created freehand on writing paper conforming to ISO standards. The low gloss of the colored film was visually evaluated based on the following evaluation criteria. Evaluation criteria: A: The colored film has no gloss and possesses sufficient low gloss. B: The colored film has a slight gloss and its low gloss is somewhat weak. C: The colored film has a glossy appearance. 【0050】 【0051】 【0052】 As is clear from the results in Table 1 above, the aqueous ink compositions for ballpoint pens of Examples 1 to 12 of this disclosure and the aqueous ballpoint pens equipped with them, compared to the aqueous ink compositions for ballpoint pens of Comparative Examples 1 to 5, which are outside the scope of this disclosure, provide highly colored lines when writing on black paper or the like without being affected by the color of the background, and also achieve a high degree of compatibility between 1) resistance to pigment sedimentation, 2) ink followability when writing quickly, 3) color development on the paper surface, and 4) low gloss lines. Furthermore, as is clear from the results in Table 2 above, the aqueous ink compositions for writing instruments and marking pens equipped with them in each of Examples 13 to 24 of this disclosure, compared to the aqueous ink compositions for writing instruments and marking pens equipped with them in Comparative Examples 6 to 10, which are outside the scope of this disclosure, yield highly colored lines when writing on black paper or the like without being affected by the color of the background, and, as described above, can be obtained as aqueous ink compositions for marking pens and marking pens that can highly balance the following characteristics: 1) resistance to pigment sedimentation, 2) ink followability when writing quickly, 3) color development on the paper surface, and 4) low gloss of the lines. 【0053】 It can be suitably used in aqueous ink compositions for writing instruments such as ballpoint pens and marking pens.

Claims

1. An aqueous ink composition for writing instruments, characterized in that it contains at least a colorant, a neutralized product of isobutylene-maleic anhydride copolymer (A), a fibrous polysaccharide (B), and water, wherein the mass ratio (A) / (B) of the neutralized product of isobutylene-maleic anhydride copolymer (A) to the fibrous polysaccharide (B) is 0.5 to 20.

2. The aqueous ink composition for writing instruments according to claim 1, further comprising 0.03 to 2% by mass of an anionic or nonionic surfactant.

3. The viscosity of the ink in the aqueous ink composition for writing instruments is such that the shear rate is 38.3 s. －１ The aqueous ink composition for writing instruments according to claim 1 or 2, characterized in that the pressure is 10 to 550 mPa·s.

4. A writing instrument characterized by being equipped with the aqueous ink composition for writing instruments described in claim 1 or 2.

Images