Aqueous ink composition and fiber core type writing instrument

Abstract

To provide an aqueous ink composition for a fiber core type writing instrument which exhibits excellent sedimentation prevention and high ink followability, and a fiber core type writing instrument using the composition.SOLUTION: The present invention provides an aqueous ink composition for a fiber core type writing instrument, the aqueous ink composition comprising high specific gravity particles having a specific gravity of 1.8 or less, a polyamide-based resin, a fatty acid amide, and biological nanofibers. The present invention also provides a fiber core type writing instrument comprising a tubular main body, a fabric ink absorbing body which is embedded in the main body and is impregnated with an aqueous ink, and a core which is provided on the front end side of the main body such that the core is in contact with the ink absorbing body, wherein the aqueous ink contains high specific gravity particles having a specific gravity of 1.8 or more, a polyamide-based resin, a fatty acid amide, and biological nanofibers.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an aqueous ink composition for a padded writing instrument, and to a padded writing instrument using the ink composition. [Background technology]

[0002] In general, metallic pigments such as aluminum powder, copper powder, and titanium oxide are blended in ink compositions used in marking pen inks to improve hiding power and obtain opacity of handwriting. Metallic pigments have high hiding power and metallic luster, but have a high specific gravity and are prone to settling. When the pigment settles, the content of the pigment in the ink discharged from the pen tip decreases due to capillary action, resulting in the discharge of ink with poor hiding power and metallic luster, which may cause problems such as insufficient opacity and metallic luster of handwriting. In particular, in aqueous ink compositions, a solvent mainly composed of water is used, so the specific gravity difference with the pigment is large, and the pigment is prone to settling in the ink, which makes the above problem more pronounced.

[0003] A method of suppressing the settling of particles with a large specific gravity such as metallic pigments includes a method of blending an anti-settling agent into an ink composition. For example, Patent Document 1 discloses an ink composition blended with an anti-settling agent, which contains water, a colorant, a polyamide resin, and a fatty acid amide to suppress the settling of particles with a large specific gravity such as pigments. Patent Document 2 discloses an aqueous ink composition for writing instruments that contains water, a solvent, a metallic pigment, and a polyamide resin, and has a viscosity of 100 (mPa·s) or less at a shear rate of 38.4 (sec-1) in a 20°C environment. Patent Document 3 discloses an ink composition for writing instruments that contains a pigment, water, and biomass nanofibers, and has a viscosity of 1 to 20 mPa·s measured at 20°C using a BL type viscometer at 30 rpm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-102760 [Patent Document 2] JP 2021-102761 A [Patent Document 3] JP 2018-53182 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, as in Patent Documents 1 to 3, when an ink composition is blended with a polyamide resin (or a mixture of a polyamide resin and a fatty acid amide) or a biomass nanofiber or other anti-settling agent to a degree that provides sufficient anti-settling properties, the viscosity of the ink increases too much, resulting in problems such as reduced ink ejection from the pen tip and ink clogging at the pen tip. In particular, in the case of a padded writing instrument, a padding made of resin fiber is used as an ink absorbent, and ink is filled into this padding, so the range of ink viscosity that can be filled is narrower than that of a direct ink type writing instrument, and it is necessary to fill it with low-viscosity ink. Therefore, if a high-viscosity ink composition is used in a padded writing instrument, the ink cannot be stably ejected from the padding, and the ink tracking may deteriorate. In other words, the problems of reduced ink ejection and ink clogging caused by the thickening of the ink due to the blending of an anti-settling agent are more pronounced in padded writing instruments. In the worst case, the viscosity becomes too high and the ink cannot be filled into the padding. Furthermore, if the pen tip is a plastic core rather than a fiber core, clogging of the pen tip is more likely to occur.

[0006] Thus, there is a trade-off between the anti-settling properties of particles with a high specific gravity, such as metallic pigments (hereinafter referred to as "high specific gravity particles"), and the ejection properties of ink from the padding (ink followability), and there has been a demand for an aqueous ink composition for use with padding-type writing instruments that achieves both of these performance properties in padding-type writing instruments and combines excellent anti-settling properties with stable ink ejection properties (high ink followability).

[0007] Therefore, the present invention has been made in consideration of the above circumstances, and aims to provide an aqueous ink composition for a padded writing instrument that combines excellent anti-settling properties and high ink tracking properties, and a padded writing instrument that uses this composition. [Means for solving the problem]

[0008] As a result of extensive research to solve the above problems, the inventors discovered that by blending a mixture of a polyamide resin and a fatty acid amide, and biologically derived nanofibers, into an aqueous ink composition, it is possible to prevent the settling of high specific gravity particles, and also to ensure stable ejection of ink from the filling even when the filling is filled with the aqueous ink composition. Based on this finding, the present invention was completed.

[0009] That is, the present invention is an aqueous ink composition for a padded writing instrument, which contains high-specific-gravity particles having a specific gravity of 1.8 or more, a polyamide resin, a fatty acid amide, and biologically-derived nanofibers.

[0010] In the aqueous ink composition, the total content of the polyamide resin, the fatty acid amide, and the biological nanofibers is preferably 0.1% by mass or more and 1.4% by mass or less.

[0011] In the aqueous ink composition, the total content of the polyamide resin, the fatty acid amide, and the biological nanofibers is preferably 0.01 to 0.3 times the content of the high specific gravity particles.

[0012] In the aqueous ink composition, it is preferable that a mass ratio A / B of a total content A of the polyamide resin and the fatty acid amide to a content B of the biological nanofibers is 1.0 or more and 7.0 or less.

[0013] In the aqueous ink composition, the biological nanofibers preferably have an amide group.

[0014] In the aqueous ink composition, the high specific gravity particles may be at least one type of particles selected from the group consisting of metallic pigments, glass flake pigments, pearl pigments, microcapsule pigments, and glitter pigments.

[0015] In the aqueous ink composition, the metallic pigment may be coated with at least one coating material selected from the group consisting of silica, molybdenum, phosphates, phosphonic acids, and phosphoric acid esters.

[0016] The present invention also relates to a padded writing instrument comprising a cylindrical main body, a fibrous ink absorber built into the main body and impregnated with water-based ink, and a core attached to the front end side of the main body so as to contact the ink absorber, wherein the water-based ink is the water-based ink composition described above. Effect of the Invention

[0017] According to the present invention, by blending a mixture of a polyamide resin and a fatty acid amide with biological nanofibers, it is possible to provide an aqueous ink composition that is excellent in preventing the settling of high specific gravity particles. In addition, even when this aqueous ink composition is used as an ink for a padded writing instrument such as a marking pen, it is possible to provide an ink composition that has high ink tracking properties. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing a marking pen as an example of a padded writing instrument according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In this specification and the drawings, components with the same reference numerals have substantially the same structure or function.

[0020] [Configuration of Water-Based Ink Composition] The aqueous ink composition of the present invention is an aqueous ink composition for a pad-type writing instrument, and contains high specific gravity particles having a specific gravity of 1.8 or more, a polyamide resin, a fatty acid amide, and biological nanofibers. The aqueous ink composition of the present invention contains both a mixture of a polyamide resin and a fatty acid amide (hereinafter, sometimes referred to as an "amide-based anti-settling agent") and biological nanofibers (hereinafter, sometimes referred to as a "nanofiber-based anti-settling agent"), thereby preventing the high specific gravity particles from settling in the aqueous ink and in the pad, and enabling the ink to be stably ejected from the pad. In other words, the ink composition of the present invention has both excellent anti-settling properties and high ink tracking properties.

[0021] The composition, properties and applications of the aqueous ink composition of the present invention will be described in detail below.

[0022] (high specific gravity particles) The high specific gravity particles of the present invention are not particularly limited as long as they have a specific gravity of 1.8 or more, and are, for example, at least one type of particles selected from the group consisting of metallic pigments, glass flake pigments, pearl pigments, microcapsule pigments, and glitter (lame) pigments. Although there is no particular upper limit to the specific gravity of the high specific gravity particles, if the specific gravity is too large, there is a possibility that sedimentation in the ink cannot be prevented, so for example, it is preferable that the specific gravity of the high specific gravity particles is 10 or less.

[0023] The specific gravity in the present invention can be measured in accordance with the pycnometer method (method using a Le Chatelier pycnometer) described in JIS K0061:2022, Methods for measuring density and specific gravity of chemical products.

[0024] <Metallic pigments> Examples of metallic pigments include powders of metals, alloys, or metal oxides such as aluminum, copper, titanium oxide, brass, stainless steel, iron oxide, aluminum oxide, and zinc oxide (hereinafter, these may be referred to as "metal powders"). Pigments containing these metals may be used. More specifically, metal powders such as aluminum powder, copper powder, titanium oxide powder, brass powder, and stainless steel powder may be used as metallic pigments, and pigments in which colorants are adsorbed onto these metal powders may be used as metallic pigments. Metal powder pastes or metal powder dispersions in which metal powders such as aluminum powder and copper powder are dispersed in a surfactant, resin, solvent, or the like to form a paste may also be used as metallic pigments. Furthermore, solid (solventless) pigments in which metal powders such as aluminum powder and copper powder are processed or dispersed with a surfactant, resin, wax, or the like may also be used as metallic pigments.

[0025] Among the metallic pigments mentioned above, pigments using aluminum powder (including paste-like pigments) are preferred. This is because aluminum has a relatively low specific gravity among metals, and pigments are less likely to settle. In addition, pigments using aluminum powder have good metallic luster in handwriting, high hiding power, and excellent opacity in handwriting.

[0026] As the metallic pigment of the present invention, commercially available products may be used, for example, STAPA (registered trademark) IL HYDROLAN S 1100, S 1500 (aluminum powder paste pigments manufactured by Ecart), STANDART (registered trademark) PCR 1100 Aluminum Powder (aluminum powder paste pigments manufactured by Ecart), Alpaste (registered trademark) WXM0650, EMR-D6390, EMR-D7670 (aluminum powder paste pigments manufactured by Toyo Aluminum), Asahi Kasei Aluminum Paste FW-600, FW-610, FW-620 (aluminum powder paste pigments manufactured by Asahi Kasei), ROTOSAFE Aqua 8 309 Richgold (copper powder paste pigments manufactured by Ecart), STANDART (registered trademark) Copper Powder F 400 (copper powder pigments manufactured by Ecart), CR-50, CR-50-2 (rutile-type titanium oxide manufactured by Ishihara Sangyo Kaisha), and the like.

[0027] The metallic pigment may be coated with at least one coating material selected from the group consisting of silica, molybdenum, phosphate, phosphonic acid, and phosphoric acid ester. By coating the metallic pigment with the coating material, as described below, the metallic pigment is easily incorporated into the gaps of the three-dimensional network structure formed by the polyamide resin and the fatty acid amide, so that the sedimentation prevention of the metallic pigment can be improved. In addition, when the metallic pigment coated with the coating material is incorporated into the three-dimensional network structure, it also has the effect of suppressing the thickening of the aqueous ink composition caused by the polyamide resin and the fatty acid amide. Therefore, the viscosity of the aqueous ink composition can be kept low, so that the ink followability can be improved. Among the above coating materials, in particular, phosphoric acid ester is preferable because it has both excellent dispersant-like and wetting agent-like functions. Here, regarding the dispersant-like function, when the metallic pigment is coated with the phosphoric acid ester, it becomes a pseudo-giant molecule, and by having steric hindrance, it is possible to suppress the aggregation of each giant molecule, and the dispersibility of the metallic pigment is improved. In terms of wetting function, since the molecular structure of the phosphate ester contains hydrophilic and hydrophobic chains, it has the same effect as a surfactant, which will be described later.

[0028] The amount of coating of the coating material is preferably 3 to 30 parts by mass when the mass of the metallic pigment is 100 parts by mass. If the amount is less than 3 parts by mass, it is difficult for the coating material to cover the entire surface of the metallic pigment, and the above-mentioned effect may not be obtained. On the other hand, if the amount exceeds 30 parts by mass, the coating material becomes excessive relative to the metallic pigment, and the excess coating material (that did not cover the metallic pigment) may precipitate in the aqueous ink, causing adverse effects.

[0029] <Glass flake pigment> The glass flake pigment is a pigment in which glass flakes are coated with a metal by plating or the like. Examples of commercially available glass flake pigments include Metashine (registered trademark) ME2025PS, MC2040PS, MC2080PS (all of which are silver-coated glass flakes manufactured by Nippon Sheet Glass Co., Ltd.), Metashine MC2080GP, MC2040GP (all of which are gold-coated glass flakes manufactured by Nippon Sheet Glass Co., Ltd.), Metashine MC1120RS, MC1080RS, MC1040RS (all of which are titanium oxide-coated glass flakes manufactured by Nippon Sheet Glass Co., Ltd.), Metashine MC1080TY (titanium oxide / iron oxide-coated glass flakes manufactured by Nippon Sheet Glass Co., Ltd.), and Metashine MC1080KR (iron oxide-coated glass flakes manufactured by Nippon Sheet Glass Co., Ltd.).

[0030] <Pearl pigment> Pearl pigments are a type of luster pigment that exhibit a pearl-like luster by utilizing the phenomenon of multiple reflection and interference of light in a thin film. Currently, the pearl pigments that are mainly distributed are titanium oxide-coated mica, which uses mica flake particles as a base material and is coated with titanium oxide microcrystals on the surface. Commercially available pearl pigments include, for example, Twinkle Pearl (registered trademark) SXA (titanium oxide-coated synthetic mica manufactured by Nihon Koken Kogyo Co., Ltd.), Iriodin (registered trademark) 100, 110, and 111 (titanium oxide-coated natural mica manufactured by Merck), and Iriodin 6111 (titanium oxide-coated synthetic mica manufactured by Merck).

[0031] <Microcapsule pigment> The microencapsulated pigment is a pigment in which colored resin particles colored with a dye or a colorant dispersed in a medium is encapsulated or solid-dissolved in a capsule (shell) made of resin (microencapsulated). Examples of the material of the capsule membrane include resins such as epoxy resin, urea resin, urethane resin, isocyanate resin, and amino resin. Examples of methods for microencapsulating colored resin particles or colorants include interfacial polymerization, interfacial polycondensation, in situ polymerization, liquid curing coating, phase separation from an aqueous solution, phase separation from an organic solvent, melt dispersion cooling, air suspension coating, and spray drying, and may be appropriately selected depending on the application. As the microencapsulated pigment, commercially available products may be used, such as Sunny Color (registered trademark) bead powder and slurry (all manufactured by Recording Material Research Institute).

[0032] <Glitter pigment> Glitter pigments (also called "lame pigments") are pigments using resin-coated metal flakes, and are formed by depositing resin on a thin metal film such as metal foil, and coating the surface of the thin metal film with a resin layer. The resin layer is preferably formed on both sides of the thin metal film. The resin layer may also contain a colorant. For example, aluminum foil can be used as the thin metal film. Examples of commercially available glitter pigments include the LG neo (registered trademark) series manufactured by Oike Kogyo Co., Ltd. and the Diamond Peace (registered trademark) series manufactured by Diamond Kogyo Co., Ltd.

[0033] <Content> The above-mentioned high specific gravity particles may be used alone or in combination of two or more kinds, but the content of the high specific gravity particles of the present invention is preferably 1 to 25% by mass with respect to the entire aqueous ink composition. If the content of the high specific gravity particles is less than 1% by mass, the effect of adding the high specific gravity particles (for example, expression of hiding property, opacity, metallic luster, etc. by pigment) may not be obtained. On the other hand, if the content of the high specific gravity particles exceeds 25% by mass, the high specific gravity particles may not have sufficient anti-settling property, and the high specific gravity particles may settle in the aqueous ink composition. In order to further improve the anti-settling property of the high specific gravity particles, the content of the high specific gravity particles is more preferably 1 to 15% by mass, and even more preferably 1 to 10% by mass.

[0034] (Polyamide resins and fatty acid amides) The polyamide resin and fatty acid amide (amide-based anti-settling agent) of the present invention are used to stabilize the dispersion of high specific gravity particles in an aqueous ink composition and suppress sedimentation. The polyamide resin is a resin having a hydrophobic portion having an amide bond inside and a hydrophilic portion such as a carboxyl group (acid portion) at the end. The polyamide resin forms an aggregate in water by hydrophobic interaction and association by hydrogen bonding of the amide group, and the aggregates are mutually entangled to form a three-dimensional network structure. At this time, by using the polyamide resin and fatty acid amide in combination, the fatty acid amide is mutually entangled with the polyamide resin, and a three-dimensional network structure having a denser and stronger binding force is formed. The high specific gravity particles such as the metallic pigment described above are taken in and penetrate into the gaps of the three-dimensional network structure by interactions such as intermolecular forces and hydrogen bonds with the aggregates. As a result, the dispersion state of the high specific gravity particles is stabilized, and the sedimentation of the high specific gravity particles in the aqueous ink composition can be suppressed.

[0035] <Polyamide resin> The polyamide resin of the present invention is a resin having an amide bond, and includes polyamides, modified polyamides, and the like.

[0036] The polyamide used in the aqueous ink composition of the present invention is, for example, a polyamide obtained by reacting a diamine with an excess amount of a dicarboxylic acid relative to the diamine, or a mixture of a dicarboxylic acid and a monocarboxylic acid.

[0037] Diamines that can be used in the synthesis of the polyamide of the present invention include, for example, diamines having 2 to 34 carbon atoms, and examples of such diamines include ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, metaxylylenediamine, 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine, 4,4'-diaminodiphenylmethane, and dimer diamine. These diamines may be used alone or in combination of two or more. Dimer diamine is a dimer acid derivative obtained by chemically reacting the carboxyl group of dimer acid, and generally commercially available ones (having 34 carbon atoms) can be used.

[0038] Dicarboxylic acids that can be used in the synthesis of the polyamide of the present invention include, for example, dicarboxylic acids having 4 to 36 carbon atoms. Examples of such dicarboxylic acids include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, isophthalic acid, dimer acid, etc. These may be used alone or in combination of two or more. Dimer acids are obtained by dimerizing unsaturated fatty acids, and generally commercially available ones (having 36 carbon atoms) can be used. Commercially available dimer acids contain monomer acids and trimer acids in addition to dimer acids, but those with a high dimer acid content are preferred.

[0039] Monocarboxylic acids that can be used in the synthesis of the polyamide of the present invention include, for example, monocarboxylic acids having 2 to 22 carbon atoms, and examples of such monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, oleic acid, behenic acid, etc. These may be used alone or in combination of two or more.

[0040] The acid value of the polyamide of the present invention is not particularly limited, but is preferably 30-140, and more preferably 40-100, for example.

[0041] The polyamide resin of the present invention is preferably converted into a polyamide salt (e.g., a polyamide amine salt) because neutralization with a neutralizing base makes it easy to form a stable structure together with a fatty acid amide described below in the aqueous ink composition.

[0042] As the neutralizing base, either an organic base or an inorganic base can be used. Examples of the organic base include alkylamines such as ethylamine, diethylamine, and triethylamine, and alcoholamines such as ethanolamine, diethanolamine, triethanolamine, and N,N'-dimethylethanolamine. Examples of the inorganic base include sodium hydroxide, potassium hydroxide, and ammonia. These neutralizing bases may be used alone or in combination of two or more.

[0043] <Fatty acid amide> The fatty acid amide used in the aqueous ink composition of the present invention is, for example, a fatty acid amide obtained by reacting a diamine or monoamine with a monocarboxylic acid.

[0044] Diamines that can be used in the synthesis of the fatty acid amide of the present invention include, for example, diamines having 2 to 12 carbon atoms, and examples of such diamines include ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, metaxylylenediamine, 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 1,12-dodecamethylenediamine, etc. These may be used alone or in combination of two or more.

[0045] The monoamines that can be used in the synthesis of the fatty acid amide of the present invention include, for example, monoamines having 2 to 22 carbon atoms, and examples of such monoamines include ethylamine, monoethanolamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, decylamine, laurylamine, myristylamine, cetylamine, stearylamine, and behenylamine. These may be used alone or in combination. These may be used alone or in combination of two or more.

[0046] Monocarboxylic acids that can be used in the synthesis of the fatty acid amide of the present invention include, for example, monocarboxylic acids having 2 to 22 carbon atoms, and examples of such monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, oleic acid, behenic acid, etc. These may be used alone or in combination of two or more.

[0047] <Mixture of polyamide resin and fatty acid amide> In the aqueous ink composition of the present invention, when the polyamide resin and the fatty acid amide are mixed, from the viewpoint of easily and stably forming the above-mentioned three-dimensional network structure and improving the dispersibility of high specific gravity particles, etc., it is preferable to add the polyamide resin and the fatty acid amide to water or an organic solvent in advance to form a mixture of the polyamide resin and the fatty acid amide (the properties of the mixture are not particularly limited, for example, a paste, a solution, an aqueous dispersion, etc.). As such a mixture of the polyamide resin and the fatty acid amide, a commercially available product may be used, and examples of the commercially available product include Disparlon (registered trademark) AQH-800 and AQH-810 (both manufactured by Kusumoto Chemicals Co., Ltd.).

[0048] <Content> The total content of the polyamide resin and the fatty acid amide is preferably 0.05% by mass to 1% by mass with respect to the total mass of the aqueous ink composition. If the total content of the polyamide resin and the fatty acid amide is less than 0.1% by mass, the effect of preventing the settling of high specific gravity particles, other colorants, resin particles, etc. may not be obtained. If the total content exceeds 1% by mass, the aqueous ink composition is excessively thickened, and the viscosity of the aqueous ink composition becomes too high, so that the ink cannot be stably ejected from the padding, and the ink tracking may be poor. As a result, the handwriting may be rubbed off or writing may become impossible. In addition, if the viscosity of the aqueous ink composition is too high, it may not be possible to fill the padding with the aqueous ink composition. From the viewpoint of further enhancing the effect of preventing settling of the high-specific-gravity particles and the ink tracking ability, the total content of the polyamide resin and the fatty acid amide is more preferably 0.2% by mass to 0.7% by mass, even more preferably 0.3% by mass to 0.6% by mass, and most preferably 0.35% by mass to 0.5% by mass, relative to the total mass of the aqueous ink composition.

[0049] (Biological nanofibers) The biological nanofibers of the present invention are used to stabilize the dispersion of high specific gravity particles in an aqueous ink composition and suppress sedimentation, similarly to the above-mentioned amide-based anti-settling agent. The biological nanofibers of the present invention are fine fibers obtained by defibrating biological resources such as cellulose, chitin, chitosan, and silk to the nano level. The defibration method of the biological nanofibers of the present invention is not particularly limited, and may be either mechanical treatment (mechanical defibration treatment) or chemical treatment, but mechanical defibration treatment is preferred. The biological nanofibers of the present invention are fibers having a fiber diameter of 1 to 100 nm and an aspect ratio of 100 or more. The fiber diameter can be measured, for example, from an electron microscope photograph. The upper limit of the aspect ratio is not particularly limited, but is preferably 1000 or less, more preferably 300 or less. The aspect ratio is determined by the ratio of the fiber diameter to the fiber length, and the viscosity of the aqueous ink composition tends to increase as the fiber length increases. Therefore, in order to stably eject the ink from the filling material and to prevent the viscosity of the aqueous ink composition from becoming too high, it is preferable that the aspect ratio is within the above range.

[0050] The present inventors speculate as follows about the form of the biological nanofibers in the aqueous ink composition of the present invention. That is, the biological nanofibers of the present invention penetrate into the gaps of the dense three-dimensional network structure formed by the above-mentioned polyamide resin and fatty acid amide, and widen the gaps. In this way, the gaps of the three-dimensional network structure widen, so that the molecules of the polyamide resin and fatty acid amide can move easily, and the fluidity of the aqueous ink composition increases. As a result, even if this aqueous ink composition is filled into the batting, the aqueous ink composition can move easily within the batting, and stable ink ejection from the batting is possible. Due to the above mechanism, the aqueous ink composition of the present invention can exhibit high ink tracking while having excellent sedimentation prevention properties, even when used as an ink for a batting-type writing instrument.

[0051] The biological nanofibers of the present invention are not particularly limited as long as they can penetrate into the gaps in the three-dimensional mesh structure formed by the polyamide resin and the fatty acid amide, and for example, known cellulose nanofibers, chitin nanofibers, chitosan nanofibers, etc. can be used. Cellulose nanofibers are nanofibers made from plant-derived cellulose. Chitin nanofibers are nanofibers made from animal-derived chitin extracted from crustacean shells. Chitosan nanofibers are nanofibers made from chitosan, a cationic polymer obtained by deacetylating chitin.

[0052] As the biological nanofiber of the present invention, commercially available products may be used. Examples of commercially available products include BiNFi-s (registered trademark) WFo-10002, BiNFi-s IMa-10002, BiNFi-s BMa-10002, BiNFi-s AFo-10002, and BiNFi-s FMa-10002 (cellulose nanofibers manufactured by Sugino Machine Ltd.), Rheocrysta (registered trademark) (cellulose nanofiber manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Cellenpia (registered trademark) (cellulose nanofiber manufactured by Nippon Paper Industries Co., Ltd.), ELLEX (registered trademark) (cellulose nanofiber manufactured by Daio Paper Co., Ltd.), Aurovisco (registered trademark) (cellulose nanofiber manufactured by Oji Holdings Corporation), Stellafine (registered trademark) (cellulose nanofiber manufactured by Marusumi Paper Co., Ltd.), BiNFi-s Sfo-20002 (chitin nanofiber manufactured by Sugino Machine Ltd.), Chitin Nanofiber Nono (chitin nanofiber manufactured by Omura Paint Co., Ltd.), and BiNFi-s EFo-08002 (chitosan nanofiber manufactured by Sugino Machine Co., Ltd.) and the like.

[0053] The biological nanofibers used in the aqueous ink composition of the present invention may be directly incorporated into the aqueous ink composition, or may be incorporated as a dispersion in which the biological nanofibers are dispersed in a medium such as water.

[0054] Here, the biological nanofiber of the present invention is preferably one having an amide group. The biological nanofiber having an amide group is not particularly limited, but for example, chitin nanofiber. When a biological nanofiber such as chitin nanofiber is used, the amide group of the biological nanofiber interacts with the amide group of the polyamide resin and the fatty acid amide (interaction between amide groups). More specifically, the amide group located on the side chain of the chitin nanofiber and the amide group in the main skeleton of the polyamide resin and the fatty acid amide form a hydrogen bond. Then, a very large side chain derived from the chitin nanofiber is bonded to the main skeleton of the polyamide resin and the fatty acid amide. As a result, the gaps in the three-dimensional network structure formed by the polyamide resin and the fatty acid amide are larger than when other biological nanofibers are used, and the mobility of the molecules of the polyamide resin and the fatty acid amide and the degree of increase in the fluidity of the aqueous ink composition are remarkable. Therefore, when the filling is filled with an aqueous ink composition containing biological nanofibers having amide groups, such as chitin nanofibers, the aqueous ink composition becomes significantly more mobile within the filling, enabling more stable ink ejection from the filling.

[0055] Furthermore, when biological nanofibers having amide groups are used, the amount of biological nanofibers can be reduced compared to when biological nanofibers without amide groups, such as cellulose nanofibers and chitosan nanofibers, are used. This is because the above-mentioned interaction between the amide groups enhances the effect of increasing the fluidity of the aqueous ink composition, so that the effect of adding the biological nanofibers can be ensured even with a small amount of the nanofibers. When the amount of additives such as biological nanofibers is reduced, the water content in the aqueous ink composition increases, making the ink less likely to dry and allowing the amount of color pigment to be increased, thereby obtaining a writing instrument such as a marking pen of the desired color.

[0056] <Content> The content of the biological nanofibers is preferably 0.03% by mass to 0.36% by mass with respect to the total mass of the aqueous ink composition. If the content of the biological nanofibers is less than 0.03% by mass, the effect of preventing the settling of high specific gravity particles, other colorants, resin particles, etc. may not be obtained. If the content exceeds 0.36% by mass, the aqueous ink composition is excessively thickened, and the viscosity of the aqueous ink composition becomes too high, so that the ink cannot be stably ejected from the padding, and the ink tracking may be poor. As a result, the handwriting may be rubbed off or writing may become impossible. In addition, if the viscosity of the aqueous ink composition is too high, it may not be possible to fill the padding with the aqueous ink composition. From the viewpoint of further enhancing the anti-settling effect of the high specific gravity particles and the ink tracking ability, the content of the biological nanofibers is more preferably 0.05% by mass to 0.21% by mass, even more preferably 0.08% by mass to 0.18% by mass, and most preferably 0.12% by mass to 0.15% by mass, relative to the total mass of the aqueous ink composition.

[0057] (Total content of anti-settling agents) The total content of the above-mentioned amide-based anti-settling agent (polyamide-based resin and fatty acid amide) and nanofiber-based anti-settling agent (biological nanofiber) is preferably 0.1% by mass or more and 1.4% by mass or less. If the total content is less than 0.1% by mass, the anti-settling effect of high specific gravity particles, other colorants, resin particles, etc. may not be obtained. In addition, as a result of not obtaining the anti-settling effect, when the ink composition is filled into the inner cotton and writing is performed, the high specific gravity particles such as pigments may also settle inside the inner cotton and / or the pen tip, which may affect the writing feel (flow) and adversely affect the ink dischargeability, which deteriorates the ink followability, and the ink followability may deteriorate. If the total content exceeds 1.4% by mass, the aqueous ink composition will be excessively thickened, and the viscosity of the aqueous ink composition will be too high, so that the ink cannot be stably discharged from the inner cotton, and the ink followability may be poor. As a result, the handwriting may be rubbed off or writing itself may become impossible. In addition, if the viscosity of the aqueous ink composition is too high, it may not be possible to fill the padding with the aqueous ink composition. From the viewpoint of further enhancing the anti-settling effect of the high specific gravity particles, it is more preferable that the content is 0.2% by mass or more and 0.8% by mass or less, even more preferable that the content is 0.3% by mass or more and 0.8% by mass or less, and most preferable that the content is 0.4% by mass or more and 0.8% by mass or less. From the viewpoint of further enhancing the ink tracking property, the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent is more preferably 0.2% by mass or more and 0.8% by mass or less, even more preferable that the content is 0.3% by mass or more and 0.7% by mass or less, and most preferable that the content is 0.4% by mass or more and 0.6% by mass or less, based on the total mass of the aqueous ink composition. From the viewpoint of combining excellent anti-settling effect and ink tracking property, it is more preferably 0.3% by mass or more and 0.7% by mass or less, even more preferable that the content is 0.4% by mass or more and 0.7% by mass or less, and most preferable that the content is 0.4% by mass or more and 0.6% by mass or less.

[0058] (Ratio of total content of anti-settling agent to content of high specific gravity particles) In addition, the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent is preferably 0.01 times or more and 0.3 times or less than the content of the high specific gravity particles. If it is less than 0.01 times, the anti-settling effect of the high specific gravity particles may not be obtained. If it exceeds 0.3 times, the aqueous ink composition is excessively thickened, and the viscosity of the aqueous ink composition becomes too high, so that the ink cannot be stably discharged from the padding, and the ink tracking may be poor. As a result, the handwriting may be rubbed off or writing may become impossible. In addition, if the viscosity of the aqueous ink composition is too high, it may not be possible to fill the padding with the aqueous ink composition. From the viewpoint of further enhancing the anti-settling effect of the high specific gravity particles, the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent is more preferably 0.03 times or more and 0.15 times or less, more preferably 0.05 times or more and 0.15 times or less, and most preferably 0.07 times or more and 0.15 times or less, of the content of the high specific gravity particles. From the viewpoint of further enhancing the ink tracking property, the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent is more preferably 0.03 times or more and 0.15 times or less, more preferably 0.05 times or more and 0.12 times or less, and most preferably 0.07 times or more and 0.10 times or less, of the content of the high specific gravity particles. From the viewpoint of combining excellent anti-settling effect and ink tracking property, it is more preferably 0.05 times or more and 0.12 times or less, more preferably 0.07 times or more and 0.12 times or less, and most preferably 0.07 times or more and 0.10 times or less.

[0059] (Ratio of amide-based anti-settling agent to nanofiber-based anti-settling agent) The mass ratio A / B of the total content A of the amide-based antisettling agent (polyamide-based resin and fatty acid amide) to the content B of the nanofiber-based antisettling agent (biological nanofiber) is preferably 1.0 or more and 7.0 or less. If the value of A / B is less than 1.0, that is, if the amount of the amide-based antisettling agent is too small, a large amount of the nanofiber-based antisettling agent is required to obtain sufficient antisettling properties, so that the amount of water in the aqueous ink composition decreases and the ink may be easily dried. On the other hand, if the value of A / B exceeds 7.0, that is, if the amount of the amide-based antisettling agent is too large, the aqueous ink composition thickens excessively, and the viscosity of the aqueous ink composition becomes too high, so that the ink cannot be stably ejected from the batting, and the ink tracking may be poor. As a result, the handwriting may be rubbed off or writing may become impossible. In addition, if the viscosity of the aqueous ink composition is too high, it may not be possible to fill the aqueous ink composition into the batting at all. From the viewpoint of suppressing drying of the ink and further enhancing ink tracking ability, the value of A / B is more preferably 1.4 or more and 7.0 or less, even more preferably 1.5 or more and 6.3 or less, and even more preferably 2.3 or more and 5.9 or less.

[0060] (Other components in the aqueous ink composition) The aqueous ink composition of the present invention may contain other components than the above-mentioned components (high specific gravity particles, amide-based anti-settling agent, nanofiber-based anti-settling agent) to the extent that the anti-settling property and ink tracking property are not impaired. Examples of other components include colorants (not included in the above-mentioned high specific gravity particles), moisturizers, surfactants, preservatives, dispersants, solvents, resin particles, etc. Furthermore, the aqueous ink composition of the present invention may contain a pH adjuster, a chelating agent, etc., as necessary.

[0061] <Coloring agent> The colorant used in the aqueous ink composition of the present invention is not particularly limited, and either a pigment or a dye can be used. As the pigment, both inorganic and organic pigments can be used, and there is no particular limitation. As the colorant of the present invention, for example, carbon black, aniline black, ultramarine, yellow lead, azo pigments, phthalocyanine pigments, quinacridone pigments, quinophthalone pigments, threne pigments, triphenylmethane pigments, anthraquinone pigments, dioxane pigments, indigo pigments, thioindigo pigments, perinone pigments, perylene pigments, isoindolene pigments, azomethine pigments, etc. can be used. In addition, as the pigment, processed pigments, fluorescent pigments, phosphorescent pigments, complementary color pigments, etc. may be used.

[0062] The dye is not particularly limited as long as it is soluble in the solvent, and examples of the dye that can be used include direct dyes, acid dyes, basic dyes, metal-containing dyes, and various salt-forming dyes. Specifically, water-soluble dyes such as triphenylmethane dyes, xanthene dyes, anthraquinone dyes, and copper phthalocyanine dyes may be used.

[0063] These pigments and dyes may be used alone or in combination of two or more. The content of the colorant is not particularly limited, but may be, for example, 0.5 to 20% by mass relative to the total mass of the aqueous ink composition.

[0064] <Moisturizer> The humectant has the role of preventing the aqueous ink composition from drying and improving the ejection properties of the ink from a writing instrument, and therefore, the humectant is preferably contained in an amount of 5% by mass to 30% by mass relative to the total mass of the aqueous ink composition.

[0065] The moisturizing agent usable in the present invention is not particularly limited, and examples thereof include polyhydric alcohol solvents, monohydric alcohol solvents, amine organic compounds, glycol ether solvents, etc., as exemplified below. Examples of the polyhydric alcohol solvents include ethylene glycol, diethylene glycol, 1,3-propanediol, triethylene glycol, propylene glycol, glycerin, etc. Examples of the monohydric alcohol solvents include methanol, ethanol, 1-propanol, 2-propanol, 2-methylpropyl alcohol (isobutanol), t-butanol, 2-propyn-1-ol (propargyl alcohol), 2-propen-1-ol (allyl alcohol), 3-methyl-1-butyn-3-ol, 3-methoxy-3-methyl-1-butanol, and other higher alcohols. Examples of the amine organic compounds include trimethylglycine, 2-pyrrolidone, N-vinylpyrrolidone, urea, etc. Examples of the glycol ether solvent include ethylene glycol monomethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol methyl ether, diethylene glycol monohexyl ether polyethylene glycol (PEG), ethylene glycol monomethyl ether acetate, etc. These moisturizing agents may be used alone or in combination of two or more.

[0066] <Surfactant> The surfactant has the role of improving the wettability of the aqueous ink composition to the writing medium and dispersing the resin particles well in water. Examples of surfactants that can be used in the present invention include nonionic surfactants such as acetylene glycol surfactants and polyoxyethylene alkyl ether surfactants. Examples of commercially available acetylene glycol surfactants include Surfynol (registered trademark) 420, 440, 465, 485 and Olfine (registered trademark) EXP.4200, EXP.4300, E1010, E1004 (all manufactured by Nissin Chemical Industry Co., Ltd.). Examples of commercially available polyoxyethylene alkyl ether surfactants include Noigen (registered trademark) P, Noigen HC, Noigen P-430 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). In the present invention, the content of the surfactant is not particularly limited, but is, for example, in the range of 0.2% by mass or more and 3% by mass or less with respect to the entire aqueous ink composition. If the content of the surfactant is less than 0.2% by mass, the effect of adding the surfactant may be insufficient. On the other hand, if the surfactant content exceeds 3 mass %, the ink ejection properties will decrease due to the viscosity dependency of the surfactant (the viscosity of the aqueous ink composition will increase), which may result in a decrease in hiding power or rubbing of letters.

[0067] <Preservatives> Examples of preservatives include organic nitrogen-sulfur compounds such as 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, 2-pyridinethiol-1-oxide sodium, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and 2-n-octyl-4-isothiazolin-3-one; phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, and propyl paraoxybenzoate.

[0068] <Dispersant> Dispersants are used for the purpose of suppressing the settling or aggregation of high specific gravity particles and other pigments, and improving the fixation of handwriting. Examples of dispersants that can be used in the present invention include phosphate ester amine salts (commercially available products include Disparlon (registered trademark) AQH-340 manufactured by Kusumoto Chemical Industries, Ltd.), carboxyl group-containing polymers (commercially available products include Flowlen (registered trademark) GW-1500 manufactured by Kyoeisha Chemical Industries, Ltd.), and block copolymers that have affinity for pigments (commercially available products include DISPERBYK (registered trademark) 190, 191, 193, etc. manufactured by BYK).

[0069] <Solvent> Although water is used as the solvent for the aqueous ink composition, a water-soluble organic solvent may be used in combination with water. The water is not particularly limited, and examples of the water that can be used include tap water, ion-exchanged water, distilled water, and ultrafiltered water.

[0070] <Resin particles> Resin particles that can be used in the aqueous ink composition of the present invention are not particularly limited, and examples thereof include olefin resin particles such as polyethylene resin and polypropylene resin, nitrogen-containing resin particles containing nitrogen atoms in the chemical structure such as melamine-formaldehyde resin, benzoguanamine-formaldehyde resin, benzoguanamine-melamine-formaldehyde resin, urea-formaldehyde resin, nylon resin, acrylic resin particles, styrene resin particles, epoxy resin particles, urethane resin particles, cellulose resin particles, etc. These resin particles may be used alone or in combination of two or more kinds.

[0071] (Uses of the aqueous ink composition) The aqueous ink composition of the present invention having the composition described above is preferably used as an ink for writing instruments such as marking pens. Here, the term "marking pen" refers to a pen that induces ink from a so-called wadding-type or direct ink-type ink reservoir to the tip of the pen by capillary action. In addition, since the aqueous ink composition of the present invention has a low viscosity as described above, it can be particularly preferably used as an ink for wadding-type marking pens. If it becomes possible to use it as an ink for wadding-type marking pens, there are the following advantages. First, direct ink-type marking pens tend to be expensive because of the large number of parts, but wadding-type marking pens can be manufactured at low cost because the number of parts can be reduced. Second, wadding-type marking pens can be filled with a larger amount of ink than writing instruments such as ballpoint pens, so that the writing distance tends to be longer. Third, since most of the marking pens using conventional opaque inks were direct ink-type, the ink contained in the ink reservoir was stirred by shaking the pen, and then the ink was finally ejected and writing became possible after knocking. In contrast, with a batting-type marking pen, you can start writing immediately without having to stir the ink or knock it, etc. Fourth, batting-type marking pens provide a smoother writing experience than ballpoint pens, ink-filled marking pens, and other writing instruments.

[0072] [Method of manufacturing water-based ink composition] The composition of the aqueous ink composition of the present invention has been described in detail above. Next, a method for producing the aqueous ink composition having the above-mentioned composition will be described.

[0073] The aqueous ink composition of the present invention can be obtained by adding components such as high specific gravity particles, amide-based antisettling agents, nanofiber-based antisettling agents, and, if necessary, color pigments other than high specific gravity particles, moisturizers, surfactants, preservatives, and dispersants to a solvent (dispersion medium) such as water, and mixing and stirring these components to disperse or dissolve them in the solvent. There are no particular limitations on the stirring method, and stirring devices such as mechanical stirrers and magnetic stirrers can be used, for example.

[0074] [Writing instrument composition] Next, the configuration of a padded marking pen 10 (hereinafter, simply referred to as "marking pen 10") as an example of a writing instrument according to a preferred embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing an outline of the configuration of a padded marking pen 10 as an example of a writing instrument according to this embodiment.

[0075] 1, the padded marking pen 10 includes a main body shaft 11 as an example of a main body of the present embodiment, padding 13 as an example of an ink absorber of the present embodiment, and a pen tip 15 as an example of a core of the present embodiment. As described below, ink impregnated in the padding 13 is transferred from the padding 13 to the pen tip 15 by capillary action, and writing can be performed by applying the pen tip 15 to the writing surface of a writing medium.

[0076] (Configuration of main body shaft 11) Main body shaft 11 has a cylindrical shape and contains padding 13. The material of main body shaft 11 is not particularly limited and may be plastic, glass, metal, or the like.

[0077] (13 padding configurations) The padding 13 is built into the main body shaft 11 and is impregnated with the above-mentioned aqueous ink composition. The padding 13 is obtained by converging long resin fibers and forming them into a cylindrical shape while causing them to crimp. The padding 13 has a porosity within a range of 80% to 95% in order to improve ink ejection properties. In this way, the marking pen 10 has a high porosity of the padding 13 and a low density of the fibers that make up the padding 13, which prevents resin particles and colorant from being caught in gaps between the fibers and preventing them from being ejected from the pen tip 15.

[0078] The fiber diameter of the resin fibers constituting the filling 13 is preferably within the range of 3 denier to 5 denier. This allows the filling 13 to have a high porosity within the above range. More preferably, the fiber diameter is 3.5 denier or more, and even more preferably, the fiber diameter is 4 denier or more. Note that the resin fibers constituting the filling 13 may be a combination of resin fibers having two or more different fiber diameters.

[0079] (Pen tip 15 configuration) The pen tip 15 is attached to the front end side of the main body shaft 11 so that its rear end contacts the tip of the inner batting 13. A part of the pen tip 15 is housed inside the main body shaft 11, but the tip is exposed to the outside from a hole (not shown) at the tip of the main body shaft 11. The material of the pen tip 15 is not particularly limited, and is, for example, fiber or plastic. The pen tip 15 has a porosity in the range of 55% to 75% inclusive in order to improve ink ejection properties. In this way, in the marking pen 10, the porosity of the pen tip 15 is relatively high, and when the pen tip 15 is made of resin fiber, the density of the resin fiber is low, so that it is possible to prevent high specific gravity particles and other colorants from being caught in the gaps between the fibers and being prevented from being ejected from the pen tip 15. It is preferable that the porosity of the pen tip 15 is smaller than the porosity of the inner batting 13. This allows the high specific gravity particles and other colorants in the aqueous ink composition to be guided to the pen tip by a strong capillary force.

[0080] In addition, since the high specific gravity particles of the present invention have a large specific gravity of 1.8 or more, depending on the climate, the state of use, and other conditions, some of the high specific gravity particles in the aqueous ink composition may settle in the padding 13. Even in such a case, in order to minimize color unevenness when writing with a writing instrument using the ink composition of the present invention, it is preferable that both the padding 13 and the pen tip 15 contain resin fibers as their materials, and that the fiber diameter of the resin fiber of the padding 13 is larger than the fiber diameter of the resin fiber of the pen tip 15. Normally, in a marking pen, resin fibers with the same fiber diameter are used for the padding and the pen tip, but by making the fiber diameter of the resin fiber of the padding 13 larger than the fiber diameter of the resin fiber of the pen tip 15 (using thicker fibers), the ink can be guided to the pen tip by a stronger capillary force. As a result, even if some of the resin particles in the aqueous ink composition settle in the padding 13, the high specific gravity particles can be more reliably guided to the pen tip 15 and ejected from the pen tip 15. Furthermore, in the aqueous ink composition of the present invention, by using an amide-based anti-settling agent in combination with a nanofiber-based anti-settling agent, the viscosity of the aqueous ink composition can be prevented from becoming too high. Therefore, even if a plastic pen tip 15 is used, clogging of the pen tip and deterioration of ink ejection performance can be suppressed.

[0081] [Writing instrument manufacturing method] The marking pen 10 having the above-mentioned configuration can be manufactured, for example, as follows.

[0082] First, ink (the aqueous ink composition of the present invention described above) is filled into the batting 13 to form a dyed batting. Next, this dyed batting is loaded into the inside of the cylindrical main body 11, and the rear end of the main body 11 is plugged. After that, the pen tip 15 is inserted from the tip of the main body 11, and a cap is loaded onto the tip. Here, the batting 13 and the pen tip 15 can be manufactured, for example, as follows.

[0083] (Manufacturing method of filling 13) First, resin fibers (e.g., long fibers) that will be the material for the filling 13 are bundled to form a fiber bundle, and the fiber bundle is fed into a mold (outer cover) while being crimped, and is heat-fused while the outer diameter of the outer cover is narrowed to adjust the size. The fused fiber bundle is then cooled. The cooled fiber bundle is cut to a desired length to produce the filling 13.

[0084] (Manufacturing method of pen tip 15) A number of threads (e.g., threads made of resin fibers such as polyester fibers, acrylic fibers, nylon fibers, etc.) are bundled together, wound around a bobbin, and passed through a pen tip manufacturing machine. The bundle of threads that has passed through the manufacturing machine is heated and formed into a cylindrical shape. Next, the cylindrical bundle of threads is impregnated with a binder resin (e.g., urethane resin, acrylic resin, etc.). The cylindrical bundle of threads impregnated with the resin is placed in a drying oven or the like to dry and harden the resin, resulting in an original rod. Finally, the original rod is cut to the desired length and the tip is ground to produce pen tip 15.

[0085] Although the preferred embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited to the above-mentioned embodiment. In other words, it is understood that other embodiments or various modifications that can be conceived by a person skilled in the art within the scope of the invention described in the claims also belong to the technical scope of the present invention.

[0086] For example, the technical scope of the present invention includes the following inventions. (1) An aqueous ink composition for a pad-type writing instrument, comprising: high-density particles having a specific gravity of 1.8 or more; a polyamide resin; a fatty acid amide; and biological nanofibers. (2) The aqueous ink composition according to (1), wherein the total content of the polyamide resin, the fatty acid amide, and the biological nanofibers is 0.1% by mass or more and 1.4% by mass or less. (3) The aqueous ink composition according to (1) or (2), wherein the total content of the polyamide resin, the fatty acid amide, and the biological nanofibers is 0.01 to 0.3 times the content of the high specific gravity particles. (4) The aqueous ink composition according to any one of (1) to (3), wherein the mass ratio A / B of the total content A of the polyamide resin and the fatty acid amide to the content B of the biological nanofibers is 1.0 or more and 7.0 or less. (5) The aqueous ink composition according to any one of (1) to (4), wherein the biological nanofibers have an amide group. (6) The aqueous ink composition according to any one of (1) to (5), wherein the high specific gravity particles are at least one type of particles selected from the group consisting of metallic pigments, glass flake pigments, pearl pigments, microcapsule pigments, and glitter pigments. (7) The aqueous ink composition according to claim (6), wherein the metallic pigment is coated with at least one coating material selected from the group consisting of silica, molybdenum, phosphates, phosphonic acids, and phosphoric acid esters. (8) A padded writing instrument comprising a cylindrical main body, a fibrous ink absorber built into the main body and impregnated with water-based ink, and a core attached to the front end side of the main body so as to contact the ink absorber, wherein the water-based ink contains high-specific-gravity particles having a specific gravity of 1.8 or more, a polyamide resin, a fatty acid amide, and biological nanofibers. (9) The padded writing instrument according to (8), wherein the total amount of the polyamide resin, the fatty acid amide, and the biological nanofibers is 0.1% by mass or more and 1.4% by mass or less. (10) The padded writing instrument according to (8) or (9), wherein the total content of the polyamide resin, the fatty acid amide and the biological nanofibers is 0.01 to 0.3 times the content of the high specific gravity particles. (11) A padded writing instrument described in any one of (8) to (10), in which the mass ratio A / B of the total amount A of the polyamide resin and the fatty acid amide to the amount B of the biological nanofibers is 1.0 or more and 7.0 or less. (12) The padded writing instrument according to any one of (8) to (11), wherein the biological nanofiber has an amide group. (13) The padded writing instrument according to any one of (8) to (12), wherein the high specific gravity particles are at least one type of particles selected from the group consisting of metallic pigments, glass flake pigments, pearl pigments, microcapsule pigments, and glitter pigments. (14) The padded writing implement according to (13), wherein the metallic pigment is coated with at least one coating material selected from the group consisting of silica, molybdenum, phosphates, phosphonic acid, and phosphoric acid esters. EXAMPLES

[0087] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following, unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass".

[0088] [Experimental Example 1] In this Experimental Example 1, aqueous ink compositions of Examples and Comparative Examples were produced as described below, and the anti-settling properties of the produced aqueous ink compositions were evaluated.

[0089] (Production of Water-Based Ink Composition) First, the aqueous ink compositions of the examples and comparative examples were produced as follows. The "Disparlon AQH-800" used as the amide-based anti-settling agent is a paste of a mixture containing polyamide amine salt and fatty acid amide, and the content of the active ingredient (polyamide amine salt and fatty acid amide) is 10%. The "Chitin Nanofiber Nono" used as the nanofiber-based anti-settling agent is a water dispersion of chitin nanofiber, and the content of the active ingredient (chitin nanofiber) is 3%. Similarly, the "BiNFi-s Wfo-10002" used as the nanofiber-based anti-settling agent is a water dispersion of cellulose nanofiber, and the content of the active ingredient (cellulose nanofiber) is 2%.

[0090] <Example 1> Deionized water 66.30 parts, triethylene glycol 10.00 parts and 1,3-propanediol 5.00 parts as moisturizing agents, acetylene glycol wetting / penetrating agent (manufactured by Nissin Chemical Industry Co., Ltd.: trade name "Olfine (registered trademark) EXP4300") 1.00 part as surfactant, organic nitrogen sulfur compound (manufactured by Osaka Gas Chemical Co., Ltd.: trade name "Slaoff (registered trademark) 72N") 0.20 parts as preservative, phosphoric acid ester amine salt (manufactured by Kusumoto Chemical Industries Co., Ltd.: trade name "Disparlon (registered trademark) AQH-340") as dispersant, mixture of polyamide amine salt and fatty acid amide (manufactured by Kusumoto Chemical Industries Co., Ltd.: trade name "Disparlon AQH-800", active ingredient amount: 10%) 3.50 parts as amide-based anti-settling agent, chitin nanofiber (manufactured by Omura Paint Co., Ltd.: trade name "Chitin Nanofiber" The mixture was mixed with 4.00 parts of fluorescein isopropyl alcohol (active ingredient amount: 3%), and the mixture was stirred for 20 minutes at 600 to 800 rpm using a stirrer (manufactured by IKA: trade name "EUROSTEAR"). Next, 3.00 parts of fluorescent pigment (manufactured by Nippon Fluorescent Co., Ltd.: trade name "Lumicol (registered trademark) NKW-6200E", specific gravity: 1.08) was mixed into the stirred mixture, and the mixture was further stirred at 600 to 800 rpm for 10 minutes. Furthermore, 6.00 parts of aluminum powder paste pigment (manufactured by Ecart: trade name "STAPA (registered trademark) IL HYDROLAN S 1100", specific gravity: 1.93) was mixed as high specific gravity particles, and the mixture was further stirred at 900 to 1000 rpm for 40 minutes to produce the aqueous ink composition of Example 1.

[0091] <Example 2> The aqueous ink composition of Example 2 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart Co., Ltd.: trade name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold, specific gravity: 8.93") was used instead of an aluminum powder paste pigment as a high specific gravity particle, the amount of Disparlon AQH-800 was 3.00 parts, cellulose nanofiber (manufactured by Sugino Machine Co., Ltd.: trade name "BiNFi-s Wfo-10002", active ingredient amount: 2%) was used instead of chitin nanofiber as a nanofiber-based sedimentation inhibitor, and no fluorescent pigment was used. The amount of water as a solvent was appropriately adjusted so that the total amount of the aqueous ink composition was 100 parts (the same applies to the following examples and comparative examples).

[0092] <Example 3> The aqueous ink composition of Example 3 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart: product name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold") was used as the high-density particle instead of the aluminum powder paste pigment, the amount of Disparlon AQH-800 was 3.00 parts, the amount of chitin nanofiber nano was 6.00 parts, and no fluorescent pigment was used.

[0093] <Example 4> The aqueous ink composition of Example 4 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart: product name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold") was used as the high-density particle instead of the aluminum powder paste pigment, and no fluorescent pigment was used.

[0094] <Example 5> The aqueous ink composition of Example 5 was produced in the same manner as in Example 1, except that a titanium oxide pigment (manufactured by Ishihara Sangyo Kaisha, Ltd.: product name "CR-50", specific gravity: 4.23) was used as the high specific gravity particle instead of the aluminum powder paste pigment, and no fluorescent pigment was used.

[0095] <Examples 6 to 10> The aqueous ink compositions of Examples 6 to 10 were produced in the same manner as in Example 1, except that the amounts of Disparlon AQH-800 and chitin nanofiber Nono were set as shown in Table 1 below.

[0096] <Example 11> The aqueous ink composition of Example 11 was produced in the same manner as in Example 1, except that 6.00 parts of cellulose nanofiber (manufactured by Sugino Machine Co., Ltd.: product name "BiNFi-s Wfo-10002") was used instead of chitin nanofiber as the nanofiber-based anti-settling agent.

[0097] <Example 12> An aqueous ink composition of Example 12 was prepared in the same manner as in Example 1, except that no dispersant was used.

[0098] <Example 13> An aqueous ink composition of Example 13 was prepared in the same manner as in Example 1, except that propylene glycol was used instead of 1,3-propanediol as the humectant.

[0099] <Example 14> An aqueous ink composition of Example 14 was prepared in the same manner as in Example 1, except that 2-pyrrolidone was used instead of triethylene glycol as the humectant.

[0100] <Example 15> An aqueous ink composition of Example 15 was prepared in the same manner as in Example 1, except that glycerin was used instead of triethylene glycol as the humectant.

[0101] <Examples 16 to 30> The aqueous ink compositions of Examples 16 to 30 were produced in the same manner as in Example 1, except that the amounts of Disparlon AQH-800 and chitin nanofiber Nono were changed to the amounts shown in Table 2 below.

[0102] <Example 31> The aqueous ink composition of Example 31 was produced in the same manner as in Example 1, except that a pearl pigment (manufactured by Nihon Koken Kogyo Co., Ltd.: product name "TWINKLE PEARL (registered trademark) SXA", specific gravity: 3.20) was used instead of the aluminum powder paste pigment as the high specific gravity particle.

[0103] <Example 32> The aqueous ink composition of Example 32 was produced in the same manner as in Example 1, except that a glass flake pigment (manufactured by Nippon Sheet Glass Co., Ltd.: trade name "Metashine (registered trademark) ME2025PS", specific gravity: 2.90) was used instead of the aluminum powder paste pigment as the high specific gravity particles.

[0104] <Comparative Example 1> The aqueous ink composition of Comparative Example 1 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart: product name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold") was used as the high specific gravity particle instead of the aluminum powder paste pigment, no fluorescent pigment or amide-based anti-settling agent was added, the amount of chitin nanofiber nano was 12.00 parts, and no fluorescent pigment was used.

[0105] <Comparative Example 2> The aqueous ink composition of Comparative Example 2 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart: product name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold") was used as the high specific gravity particle instead of the aluminum powder paste pigment, no fluorescent pigment and no amide-based anti-settling agent were added, 12.00 parts of cellulose nanofiber (manufactured by Sugino Machine: product name "BiNFi-s Wfo-10002") was used instead of chitin nanofiber as the nanofiber-based anti-settling agent, and no fluorescent pigment was used.

[0106] <Comparative Example 3> An aqueous ink composition of Comparative Example 3 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart: product name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold") was used as the high-specific-gravity particle instead of the aluminum powder paste pigment, no fluorescent pigment and no nanofiber-based anti-settling agent were added, the amount of Disparlon AQH-800 added was 6.00 parts, and no fluorescent pigment was used.

[0107] <Comparative Example 4> An aqueous ink composition of Comparative Example 4 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart: product name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold" was used as the high-specific-gravity particle instead of the aluminum powder paste pigment, the fluorescent pigment, the amide-based anti-settling agent, and the nanofiber-based anti-settling agent were not blended, 6.00 parts of an alkylol ammonium salt (manufactured by BYK: product name "ANTI-TERRA-250", active ingredient amount: 70%) was used as the anti-settling agent, and no fluorescent pigment was used.

[0108] <Comparative Example 5> The aqueous ink composition of Comparative Example 5 was produced in the same manner as in Example 1, except that a copper powder paste pigment (manufactured by Ecart: product name "ROTOSAFE (registered trademark) Aqua 8 309 Richgold" was used as the high-specific-gravity particle instead of the aluminum powder paste pigment, the fluorescent pigment, the amide-based anti-settling agent, and the nanofiber-based anti-settling agent were not blended, 0.67 parts of an alkylol ammonium salt (manufactured by BYK: product name "ANTI-TERRA-250", active ingredient amount: 70%) was used as the anti-settling agent, and no fluorescent pigment was used.

[0109] The formulations of the aqueous ink compositions of the Examples and Comparative Examples produced as described above are shown in Tables 1 to 3 below.

[0110] (Evaluation of Anti-settling Property) The aqueous ink compositions of the Examples and Comparative Examples prepared as described above were evaluated for anti-settling properties. The method and criteria for evaluating the anti-settling properties are shown below.

[0111] 100 mL of samples (sample liquid) of the aqueous ink compositions of the Examples and Comparative Examples were collected in an Eye-Boy manufactured by AS ONE Corporation. The collected sample liquid was left to stand in a thermostatic chamber at 40°C for one week, after which the state of the sample liquid was observed and the anti-settling property was evaluated according to the following evaluation criteria. The evaluation results of the anti-settling property are shown in Tables 1 to 3. A: No supernatant or precipitate B: A small amount of supernatant was observed. C: Separated into two layers (no pigment sedimentation was observed) D: The pigment had settled.

[0112] [Experimental Example 2] In this experimental example 2, a batting-type marking pen was manufactured as follows, and the batting of this marking pen was impregnated with the aqueous ink compositions of the above-mentioned Examples and Comparative Examples, and the ink tracking (ejection properties) was evaluated.

[0113] (Manufacture of cotton-filled marking pens) The water-based ink composition of the Example and Comparative Example was filled into the batting to obtain a dyed batting. The dyed batting was loaded into the inside of a resin main body, and the rear end of the main body was plugged. Next, the pen tip was inserted from the front end of the main body, and a cap was placed on the front end to produce a batting-type marking pen filled with the water-based ink composition of the Example and Comparative Example. The batting used was a product name "XER5.4x78.5 (porosity 90%)" manufactured by Unipoint Co., Ltd., and the pen tip used was a product name "PO-5S (1.5x30.0 with metal fitting tip)" manufactured by Teibow Co., Ltd.

[0114] (Ink followability evaluation: initial writing) Using a stencil-type marking pen filled with the aqueous ink composition of each of the Examples and Comparative Examples, writing was performed on plain black paper (manufactured by Etranger di Costarica, product name "BK-25-01 [B5 ring notebook Blanc de Noirs, black]"), and the ink followability was evaluated according to the following criteria. The evaluation results of the ink followability are shown in Tables 1 to 3. A: The metallic luster is sufficient and the base cannot be seen through. B: The metallic luster is low, and the base is visible. C: No metallic luster, writing marks are rubbed off D: Ink is not coming out of the padding, so writing is not possible.

[0115] (Evaluation of ink tracking: writing over time) The batting-type marking pen used for the evaluation of ink tracking was left standing with the tip facing up at room temperature for one week, and after one week, the ink tracking when written on again was evaluated according to the following criteria. The evaluation results are shown in Tables 1 to 3. A: Compared to the initial writing, there is less shading, there is a sufficient metallic luster, and the base is not visible. B: Compared to the initial writing, there is more shading, less metallic luster, and the base is visible C: The shading is much different from the initial writing, there is no metallic luster, and the writing marks have been rubbed off. D: Ink is not coming out of the padding, so writing is not possible.

[0116] [Evaluation Results] As shown in Tables 1 and 2, the aqueous ink compositions of Examples 1 to 32 had sufficient (C or higher) anti-settling properties and ink tracking properties (initial writing, aged writing). On the other hand, as shown in Table 3, the aqueous ink compositions of Comparative Examples 1 to 5, which did not contain at least one of an amide-based anti-settling agent and a nanofiber-based anti-settling agent, were poor in ink tracking properties (D rating). Furthermore, Comparative Examples 4 and 5, which did not contain either an amide-based anti-settling agent or a nanofiber-based anti-settling agent, were poor in both ink tracking properties and anti-settling properties (D rating).

[0117] As can be seen from a comparison of Examples 1, 4, 5, 31, and 32, when an aluminum powder paste pigment with a relatively low specific gravity was used as the high specific gravity particle, the anti-settling property and ink tracking property were particularly excellent. This is presumably because the higher the specific gravity of the particles contained in the aqueous ink composition, the more likely the high specific gravity particles are to settle in the ink or in the batting when the same amount of anti-settling agent is blended, and when they settle in the batting, part of the metallic pigment used as the high specific gravity particles remains in the batting, and the amount of metallic pigment ejected to the pen tip is slightly reduced.

[0118] As can be seen from a comparison between Example 1 and Examples 6 to 10, when the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent was 0.3% or more, the anti-settling properties were excellent (Rating B or higher), and when it was 0.4% or more, the anti-settling properties were particularly excellent (Rating A). On the other hand, when the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent was 0.3% or more and 0.7% or less, the ink tracking properties (writing over time) were excellent (Rating B or higher), and when it was 0.4% or more and 0.6% or less, the ink tracking properties (writing over time) were particularly excellent (Rating A).

[0119] As can be seen from the comparison of Example 1 and Examples 6 to 10, when the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent was 0.05 times or more the content of the high specific gravity particles, the anti-settling properties were excellent (evaluated as B or higher), and when it was 0.07 times or more, the anti-settling properties were particularly excellent (evaluated as A). On the other hand, when the total content of the amide-based anti-settling agent and the nanofiber-based anti-settling agent was 0.05 times or more and 0.12 times or less the content of the high specific gravity particles, the ink followability (writing over time) was excellent (evaluated as B or higher), and when it was 0.07 times or more and 0.10 times or less, the ink followability (writing over time) was particularly excellent (evaluated as A).

[0120] As can be seen from a comparison between Example 1 and Example 11, the use of chitin nanofibers having amide groups as a nanofiber-based anti-settling agent showed superior anti-settling properties and ink followability to cellulose nanofibers.

[0121] As can be seen from a comparison between Example 1 and Example 12, the ink containing a dispersant had better anti-settling properties and ink tracking properties than the ink containing no dispersant.

[0122] As can be seen from the comparison of Example 1 and Examples 16 to 30, when the ratio (A / B) of the content A of the amide-based anti-settling agent to the content B of the nanofiber-based anti-settling agent is 1.6 or more and 6.3 or less, the ink tracking property (writing over time) is excellent (evaluation B or higher), and when it is 2.9 or more and 5.6 or less, the ink tracking property (writing over time) is particularly excellent (evaluation A). It is presumed that when the ink tracking property (writing over time) is low in the range of small A / B, the ink tends to dry out a little because the amount of nanofiber-based anti-settling agent is large. It is presumed that when the ink tracking property (writing over time) is low in the range of large A / B, the ink tends to thicken a little because the amount of amide-based anti-settling agent is large, and the ink viscosity is slightly high.

[0123] [Table 1]

[0124] [Table 2]

[0125] [Table 3] [Explanation of symbols]

[0126] 10 (Filled) Marking Pen 11 Main body shaft 13 Padding 15 Pen Tip

Claims

1. An aqueous ink composition for a padded writing instrument, comprising: An aqueous ink composition comprising high-density particles having a specific gravity of 1.8 or more, a polyamide resin, a fatty acid amide, and biologically derived nanofibers.

2. The aqueous ink composition according to claim 1 , wherein the total content of the polyamide resin, the fatty acid amide, and the biological nanofibers is 0.1% by mass or more and 1.4% by mass or less.

3. The aqueous ink composition according to claim 1 , wherein a total content of the polyamide resin, the fatty acid amide, and the biological nanofibers is 0.01 to 0.3 times a content of the high specific gravity particles.

4. The aqueous ink composition according to claim 1 , wherein a mass ratio A / B of a total content A of the polyamide resin and the fatty acid amide to a content B of the biological nanofibers is 1.0 or more and 7.0 or less.

5. The aqueous ink composition according to claim 1 , wherein the biologically derived nanofibers have an amide group.

6. 2. The aqueous ink composition according to claim 1, wherein the high specific gravity particles are at least one type of particles selected from the group consisting of metallic pigments, glass flake pigments, pearl pigments, microcapsule pigments, and glitter pigments.

7. 7. The aqueous ink composition according to claim 6, wherein the metallic pigment is coated with at least one coating material selected from the group consisting of silica, molybdenum, phosphates, phosphonic acids and phosphoric acid esters.

8. A cylindrical main body portion; a fibrous ink absorber impregnated with water-based ink and incorporated in the main body; a core body attached to a front end side of the main body portion so as to contact the ink absorber; Equipped with The water-based ink of the padded writing instrument contains high-specific-gravity particles having a specific gravity of 1.8 or more, a polyamide resin, a fatty acid amide, and biological nanofibers.

9. 9. The padded writing implement according to claim 8, wherein the total amount of the polyamide resin, the fatty acid amide, and the biological nanofibers is 0.1% by mass or more and 1.4% by mass or less.

10. 9. The padded writing implement according to claim 8, wherein the total content of the polyamide resin, the fatty acid amide, and the biological nanofibers is 0.01 to 0.3 times the content of the high specific gravity particles.

11. 9. The padded writing instrument according to claim 8, wherein a mass ratio A / B of a total amount A of the polyamide resin and the fatty acid amide to an amount B of the biological nanofibers is 1.0 or more and 7.0 or less.

12. The padded writing instrument according to claim 8 , wherein the biological nanofiber has an amide group.

13. 9. The padded writing implement according to claim 8, wherein the high specific gravity particles are at least one type of particles selected from the group consisting of metallic pigments, glass flake pigments, pearl pigments, microcapsule pigments, and glitter pigments.

14. 14. The padded writing implement according to claim 13, wherein the metallic pigment is coated with at least one coating material selected from the group consisting of silica, molybdenum, phosphates, phosphonic acids, and phosphoric acid esters.

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