Aqueous ink composition for writing utensil, and writing utensil and ink cartridge incorporating the same

Abstract

To provide an aqueous ink composition for a writing utensil which has high temporal stability, prevents defects such as a thin spot in handwriting over a long period from an initial period, and enables formation of high concentration handwriting on a paper surface, and a writing utensil and an ink cartridge incorporating the same.SOLUTION: An aqueous ink composition for a writing utensil contains at least a self-dispersible pigment and a resin-dispersible pigment, and water, wherein the content of the resin-dispersible pigment to be added to the content of the self-dispersible pigment to be added is 1.5 to 12 times. There is also provided a writing utensil and an ink cartridge incorporating the aqueous ink composition for the writing utensil.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous ink composition for a writing instrument, and more particularly to an aqueous ink composition for a writing instrument that can produce handwriting of high density, and a writing instrument and an ink cartridge using the same. [Background technology]

[0002] Traditionally, pigment inks have been widely used in writing instruments such as water-based ballpoint pens because of their excellent water resistance. In particular, demand for self-dispersing pigments has been increasing in recent years because the ink exhibits high color development and can form highly dense handwriting when the ink is applied to the surface of paper. When self-dispersing pigments are used, the writing density is high, but compared to general pigments, the writing feel is deteriorated and the writing is more likely to become smudged. Therefore, a technology has been disclosed that solves this problem by using an emulsion of an acrylic resin with a glass transition temperature of 0°C or lower in combination with a surface tension adjuster (for example, see Patent Document 1). Furthermore, a technique has been disclosed in which oxidized cellulose is used in combination with a self-dispersing pigment in order to suppress blurring of handwriting (loss of drawn lines) (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5690087 [Patent Document 2] JP 2017-48274 A Summary of the Invention [Problem to be solved by the invention]

[0004] The invention of Patent Document 1 is a technology in which, when self-dispersing carbon black is used as a self-dispersing pigment, the addition of an emulsion of an acrylic resin with a glass transition temperature of 0°C or lower improves the water resistance and abrasion resistance of handwriting, and the addition of a surface tension adjuster smooths the flow of ink from the pen tip and reduces smearing of handwriting. However, since self-dispersing carbon black has poor dispersion stability, there is a risk that color unevenness will occur in handwriting in products stored for a long period of time, and that poor writing will occur when used in a ballpoint pen. The invention of Patent Document 2 is a technology that uses a self-dispersing pigment to suppress the unevenness of viscosity distribution over time (difference in viscosity between high and low) that is a problem of writing instrument inks using oxidized cellulose, and to obtain a water-based ink with excellent stability of viscosity distribution over time, and it is described that a resin-dispersed pigment can be used in combination with the self-dispersing pigment at a mass ratio of 1 / 2 or less (50 mass% or less), preferably 1 / 4 or less (25 mass% or less). This is because in an ink that has been made highly viscous by using oxidized cellulose, a resin-dispersed pigment is used in combination at the aforementioned ratio (1 / 2 or less of the self-dispersing pigment, preferably 1 / 4 or less) in order to maintain the stability of the pigment, and depending on the amount of oxidized cellulose blended and the fiber diameter, it may not be possible to ensure long-term pigment stability, and sedimentation or aggregation may occur over time.

[0005] The present invention is intended to solve the problems that arise when a self-dispersing pigment is used as a colorant, that is, to provide an aqueous ink composition for a writing instrument that has high stability over time and is capable of forming highly dense handwritten marks on a paper surface without problems such as smearing of handwritten marks from the beginning to a long period of time, and a writing instrument and an ink cartridge incorporating the same. [Means for solving the problem]

[0006] The present invention relates to an aqueous ink composition for a writing instrument, which contains at least a self-dispersion pigment, a resin-dispersion pigment, and water, and in which the content of the resin-dispersion pigment is added in an amount 1.5 to 12 times the content of the self-dispersion pigment. Further requirements include that the material contains a nonionic or anionic dispersant as a dispersant, that the material contains a phosphate ester surfactant as a lubricant, and that the viscosity at 50 rpm measured with a rotational viscometer is in the range of 1 to 5 mPa s (20°C). Further, it is required that the composition contains an antifoaming agent, and that the antifoaming agent contains at least one type selected from the group consisting of silicone-based, hydrophobic silica-based, polyether-based, acetylene glycol-based, acrylic polymer-based, oil-based, metal soap-based, and amide wax-based antifoaming agents. Further, the present invention provides a writing instrument incorporating any one of the above-mentioned water-based ink compositions for writing instruments, and an ink cartridge incorporating any one of the above-mentioned water-based ink compositions for writing instruments. Effect of the Invention

[0007] According to the present invention, a highly concentrated handwriting can be obtained using a self-dispersing pigment, and high ink stability performance can be maintained over a long period of time, resulting in an aqueous ink composition for a writing instrument that allows good writing over a long period of time without problems such as smeared handwriting, and a writing instrument incorporating the same. Furthermore, when the aqueous ink composition for writing instruments is stored in an ink cartridge, it has excellent ink tracking properties when the ink cartridge is replaced, and stable ink discharge properties can be maintained even with long-term continuous use by replacing the ink cartridge after the ink is consumed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In the ink composition of the present invention, when a self-dispersion pigment that can obtain a dense handwriting is used, an ink that can maintain stability for a long period of time without being affected by the ink viscosity was investigated, and it was found that high ink dispersion stability performance can be obtained by adding a resin-dispersion pigment in an amount 1.5 to 12 times the content of the self-dispersion pigment. In particular, it was found that higher performance can be obtained when a nonionic dispersant or an anionic dispersant is used as a dispersant for dispersing the resin-dispersion pigment.

[0009] The pigment used as the colorant is a combination of a self-dispersion type pigment and a resin-dispersion type pigment. In the present invention, the term "self-dispersing pigment" refers to a pigment that can be dispersed or dissolved in an aqueous medium without a dispersant, and the term "resin-dispersed pigment" refers to a pigment that can be dispersed by the use of a dispersant. Examples of self-dispersing pigments include pigments in which hydrophilic groups are bonded (grafted) to the surface of the pigment by subjecting the pigment to physical or chemical treatment. The hydrophilic group is preferably one or more hydrophilic groups selected from, for example, -COOM, -SO3M, -SO2M, -CO-, -OM, -SON2NH2, -RSO2M, -PO3HM, -PO3M2, -SON2NHCOR, -NH3, and -NR3. In these formulas, M each independently represents a hydrogen atom, an alkali metal, ammonium, a phenyl group which may have a substituent, or an organic ammonium. In these formulas, R each independently represents an alkyl group having 1 to 12 carbon atoms or a naphthyl group which may have a substituent. Examples of the physical treatment include vacuum plasma treatment, and examples of the chemical treatment include a wet oxidation method in which oxidation is performed with an oxidizing agent in water, a method in which a carboxyl group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface, and a method in which the pigment surface is sulfonated with a sulfonating agent such as sulfur oxide or sulfamic acid in a sulfonating solvent such as sulfolane, and then the pigment is subjected to phase inversion to an aqueous system.

[0010] Examples of the self-dispersing pigment include self-dispersing carbon black and self-dispersing organic pigments. Commercially available products include the Microjet series manufactured by Orient Chemical Industry Co., Ltd., the Aqua-Black series manufactured by Tokai Carbon Co., Ltd., the Fuji-JET Black series manufactured by Fuji Pigment Co., Ltd., and the CAB-O-JET series manufactured by Cabot Corporation. Examples of the resin-dispersed pigment include carbon black, general organic pigments, and inorganic pigments such as titanium oxide. The self-dispersing pigment may be used alone or in combination of two or more kinds.

[0011] The content of the resin-dispersed pigment is added in an amount 1.5 to 12 times the content of the self-dispersed pigment. By setting the content of the resin-dispersed pigment in the above range, the resin-dispersed pigment acts effectively on the self-dispersed pigment, maintaining dispersibility in the water-based ink, thereby obtaining long-term ink stability. If the content is less than 1.5 times, as the writing distance increases, there is a risk that the writing feel will deteriorate and the handwriting will become smudged due to wear of the ball seat, and there is a risk that color unevenness will occur after long-term storage, making it difficult to obtain a sufficient stability effect. On the other hand, if the content exceeds 12 times, it becomes necessary to reduce the content of the self-dispersing pigment so that the total pigment content does not become too large, and there is a risk that the handwriting will have poor color development, so the aforementioned range is preferable.

[0012] The content of the pigment in the ink (total of the self-dispersed pigment and the resin-dispersed pigment) is desirably in the range of 3 to 15 mass %, preferably 5 to 12 mass %, based on the total amount of the aqueous ink composition for writing instruments. By setting the content within the above range, it is possible to obtain an ink composition that is excellent in stability while forming clear handwriting.

[0013] In addition, if necessary, dyes or special pigments that are soluble or dispersible in an aqueous medium can be added. As the dyes, acid dyes, basic dyes, direct dyes, etc. can be used. Examples of special pigments include fluorescent pigments, pearl pigments, gold and silver metallic pigments, phosphorescent pigments, white pigments such as titanium dioxide, and metal powders such as aluminum.

[0014] The dispersant may be a nonionic, anionic or cationic dispersant, any of which may be used. Of these, nonionic and anionic dispersants are more preferred because they tend to be particularly excellent in dispersion stability in the configuration of the present invention. Specifically, examples of anionic dispersants include polyacrylic acid and its derivatives, acrylic acid copolymers, formalin condensates of aromatic sulfonic acids, formalin condensates of β-naphthalenesulfonic acid, etc. Examples of nonionic dispersants include ethylene oxide adducts of alkyl ethers, ethylene oxide adducts of glycerin fatty acid esters, polyvinylpyrrolidone and its derivatives, vinylpyrrolidone copolymers, etc. These dispersants can be used alone or in combination of two or more. When a dispersant is used, the content is preferably 10 to 80 mass %, and more preferably 15 to 60 mass %, based on the total mass of the pigment.

[0015] The ink composition according to the present invention comprises water. The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water. The content of water relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 35 to 95 mass %, more preferably 40 to 90 mass %.

[0016] In addition to the above-mentioned components, the ink composition of the present invention can contain optional components within a range that does not impair the effects of the present invention.

[0017] For example, conventional water-soluble organic solvents that are compatible with water can be used, such as ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, sulfolane, 2-pyrrolidone, and N-methyl-2-pyrrolidone. The water-soluble organic solvents may be used alone or in combination of two or more kinds, and are used in the range of 2 to 60% by mass, preferably 5 to 35% by mass.

[0018] Furthermore, a water-soluble resin can be added to impart adhesion and viscosity to the paper surface. Examples of the water-soluble resin include alkyd resin, acrylic resin, styrene-maleic acid copolymer, cellulose derivative, polyvinylpyrrolidone, dextrin, etc. The water-soluble resin can be used alone or in combination of two or more kinds, and is used in the range of 1 to 30 mass % in the ink composition. Polyvinyl alcohol, which is often added, is not added to the ink of the present invention because it increases the viscosity of the ink. The composition of the present invention is particularly useful for application to low viscosity inks because it can maintain the dispersion stability of the pigment without increasing the viscosity of the ink.

[0019] Furthermore, a surfactant can be blended, and the surface tension of the ink composition can be adjusted within an appropriate range. The surfactant may be a nonionic surfactant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or the like, and any of them may be suitably used. Examples of the surfactant include phosphate ester surfactants, silicone surfactants, surfactants having an acetylene bond in the structure, fluorine surfactants, etc., and these surfactants are appropriately selected depending on the components of the ink composition and the application, etc. In particular, in the configuration of the present invention, phosphate ester surfactants are preferably used because they have high affinity and also exhibit an effect as a lubricant. The content of the surfactant is not particularly limited, but is preferably in the range of 0.01 to 10% by mass, and more preferably 0.05 to 5% by mass.

[0020] Furthermore, a pH adjuster can be blended to adjust the pH of the ink composition to an appropriate range. As the pH adjuster, various acidic substances and basic substances can be used. Examples of acidic substances include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid, lactic acid, citric acid, tartaric acid, and malic acid. Examples of basic substances include ammonia, sodium carbonate, sodium hydrogen phosphate, potassium hydrogen phosphate, sodium hydroxide, potassium hydroxide, sodium acetate, etc., and also alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, etc. can be used. The content of the pH adjuster is not particularly limited, but is preferably in the range of 0.1 to 5% by mass, and more preferably 0.5 to 2% by mass. In addition, in addition to boric acid, which is usually added as an acidic substance, borate salts, diglyceryl borate and other boric acid compounds are not added to the ink of the present invention because adding them can cause problems such as pigment aggregation when a nonionic or anionic dispersant is used as a dispersant, or failure to exert lubricating function when a phosphate ester surfactant is used as a lubricant.

[0021] In addition, if necessary, rust inhibitors such as benzotriazole, tolyltriazole, 2,5-dimercapto-1,3,4-thiadiazole, and saponin, preservatives or antifungals such as phenol, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine; Wetting agents and specific gravity adjusters such as urea, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysates, and sodium pyrophosphate may also be used. Furthermore, air bubbles can be removed chemically by adding ascorbic acids, erythorbic acids, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamines, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, or the like. In addition, by adding a thickening inhibitor such as an oligomer of N-vinyl-2-pyrrolidone, an oligomer of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, or an oligomer of N-vinyl-ε-caprolactam, the functionality in the retractable form can be improved. Furthermore, a lubricant can be added, for example, metal soap, polyalkylene glycol fatty acid ester, ethylene oxide-added cationic activator, phosphate ester-based activator, β-alanine-based surfactant, N-acylamino acid, N-acylmethyltaurine, 2,5-dimercapto-1,3,4-thiadiazole, its salt or oligomer, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensate of N-acyl-L-glutamic acid and L-lysine, its salt, etc. are used. In particular, as described above, in the configuration of the present invention, phosphate ester-based surfactants are preferably used because they have high affinity. Furthermore, a shear thinning agent such as xanthan gum, welan gum, succinoglycan, guar gum, etc. may be added within a range that does not deviate from the desired viscosity.

[0022] Since the ink composition of the present invention is prone to foaming due to the ink shaking caused by the pigment dispersant, it is preferable to use a defoaming agent, particularly when the ink composition is contained in an ink cartridge for use. Examples of the defoaming agent include silicone-based, hydrophobic silica-based, polyether-based, acetylene glycol-based, acrylic polymer-based, oil-based, metal soap-based, and amide wax-based defoaming agents, and one or more of these may be selected and used. The use of a defoaming agent suppresses foaming during ink oscillation and ensures ink flowability in a small-diameter resin cartridge even for water-based inks with high surface tension, stabilizing the supply of ink to the pen tip after ink cartridge replacement and allowing for uniform handwriting over a long period of time. This means that continuous ink ejection stability is maintained even with long-term continuous use involving ink cartridge replacement.

[0023] The defoaming agent is added in an amount of 0.001 to 3% by weight, preferably 0.01 to 0.5% by weight, based on the total amount of the ink composition. If the amount is less than 0.001% by weight, it is difficult to obtain the desired effect, and if the amount exceeds 3% by weight, no improvement in the effect is observed, so there is no need to add more than this amount.

[0024] The aqueous ink composition having the above-mentioned configuration is applied in a viscosity range that allows ejection when incorporated into a writing instrument, but the ink configuration of the present invention is particularly effective in low-viscosity inks, which are considered to be disadvantageous in terms of pigment dispersion stability. Specifically, examples of inks that are difficult to obtain dispersion stability due to their ink viscosity include inks with a viscosity in the range of 1 to 5 mPa·s (20° C.) at 50 rpm as measured by a BL type rotational viscometer. The ink composition of the present invention is more effective because it can stably retain the self-dispersing pigment for a long period of time even in inks with extremely low viscosities of 1 to 5 mPa·s.

[0025] Furthermore, in the aqueous ink composition having the above-mentioned constitution, the destabilization index TSI of the self-dispersed pigment and the resin-dispersed pigment is preferably adjusted to be 0.02 to 0.2. The TSI (TURBISCAN Index) is a value calculated using the following formula, and is an index showing the instability of the pigment in the ink. TIFF2024065063000001.tif1351 (wherein h indicates the time of scanning, H indicates the measurement time, i indicates the number of scans, and scani(h) indicates the intensity of multiple scattered light during scanning.) This can be achieved by using the "TURBISCAN" liquid dispersion stability evaluation device to detect transmitted light and backscattered light from the sample by scanning a light source vertically across the sample tube at regular intervals (quantifying the degree of change in the dispersion state over time). If the instability index TSI exceeds 0.2, pigment sedimentation is likely to occur, so it is particularly desirable to keep it in the range of 0.02 to 0.2.

[0026] The aqueous ink composition for writing instruments of the present invention is filled into writing instruments such as marking pens and ballpoint pens with fiber tips, felt tips, plastic tips, fountain pen-type metal tips, and ballpoint pen tips attached to the writing tip, as well as fountain pens. In addition to being filled directly into writing instruments, the composition is filled into the ink storage section of an ink cartridge that is detachable from the main body of the writing instrument. The writing instrument may be of a cap type having a cap that covers the pen tip, or of a retractable type having a retractable mechanism such as a knock type, a rotating type, or a sliding type, and the pen tip can be stored in the barrel.

[0027] When filling a marking pen, the structure and shape of the marking pen itself are not particularly limited, and examples include a marking pen structure in which a marking pen tip such as a fiber tip, felt tip, or plastic tip (bullet type, chisel type, brush pen type, etc.) or a fountain pen type metal tip is attached to the writing tip, and ink is supplied to the writing tip by impregnating an ink occlusion body made of a fiber bundle contained inside the barrel with ink; a structure in which ink is directly contained inside the barrel and a predetermined amount of ink is supplied to the writing tip through an ink flow rate adjustment member in the shape of a comb groove or an ink flow rate adjustment member made of a fiber bundle; and a structure in which ink is directly contained inside the barrel and a valve mechanism supplies a predetermined amount of ink to the writing tip. In addition to a pen with one pen tip, it may be a double-ended pen with pen tips of different thicknesses and shapes on both ends of the barrel. In the double-ended pen, one end may be a ballpoint pen.

[0028] When filling a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited, and examples include a structure in which the ink is impregnated into an ink occlusion body made of a fiber bundle contained inside the barrel and ink is supplied to the writing tip, a structure in which the ink is directly contained inside the barrel and an ink flow rate regulator in the form of a comb groove or an ink flow rate regulator made of a fiber bundle is interposed, a ballpoint pen having an ink reservoir tube filled with the ink composition inside the barrel, the ink reservoir tube communicating with a tip having a ball attached to its tip, and a liquid plug for preventing backflow in close contact with the end face of the ink, etc. It is to be noted that a solid plug can be used in combination with the liquid plug.

[0029] The ballpoint pen tip may be, for example, one in which a ball receiving seat and ink outlet are formed inside by cutting metal, or one in which a number of inward protrusions are formed on the inner surface near the tip of a metal pipe by pressure deformation from the outside, with ink outlet gaps extending radially outward from the center between the inward protrusions. In particular, tips formed by pressure deformation have a relatively small contact area with the rear end of the ball, providing a smooth writing feel even with low writing pressure. The ball held in the ballpoint pen tip is effectively a ball made of cemented carbide, stainless steel, ruby, ceramic, etc., with an outer diameter of 0.1 to 2.0 mm, preferably 0.2 to 1.2 mm, and more preferably 0.28 to 1.0 mm. Furthermore, the ballpoint pen tip can be configured so that a resilient member is provided within the tip to resilient the rear end of the ball forward, so that when not writing, the ball is pressed against the inner edge of the tip tip to create a tight seal, and when writing, the ball is moved back by writing pressure to allow ink to flow out, thereby preventing ink leakage when not in use. The resilient member may be, for example, a thin metal wire spring, a spring with a straight portion (rod portion) at one end, or a linear plastic body, and is applied in a configuration capable of being pressed by a resilient force of 5 to 40 g.

[0030] As the barrel for accommodating the water-based ink composition, a molded article made of a thermoplastic resin such as polyethylene, polypropylene, or polyethylene terephthalate is preferably used from the standpoint of low evaporation of the ink and productivity. The tip may be directly connected to the barrel, or may be connected to the barrel and the tip via a connecting member.Furthermore, the tip may be configured as a replaceable cartridge type. When the ink composition is low viscosity, the ink composition can be stored in the barrel by attaching an ink retaining member to the front of the barrel and storing the ink composition directly in the barrel, or by impregnating a porous body or a fiber-processed body with the ink composition.

[0031] In a writing instrument using a so-called pen core, in which the ink retaining member is constituted by a number of thin disks arranged in parallel with slight gaps (comb-shaped intervals) between each other, a slit-shaped ink guide groove running vertically through the disks in the axial direction and a wider ventilation groove than the groove, and an ink guide core for guiding ink from the ink reservoir to the pen tip is disposed at the axial center, any synthetic resin that can be injection molded into a comb-shaped structure for a number of disks can be used as the material, such as general-purpose polycarbonate, polypropylene, polyethylene, acrylonitrile-butadiene-styrene copolymer, etc., but acrylonitrile-butadiene-styrene copolymer is preferable because it has particularly high moldability and is easy to obtain pen core performance.

[0032] Furthermore, the ink reservoir that is disposed behind the pen core and contains the water-based ink composition can be in the form of an ink cartridge that is detachable from the writing instrument body. In this case, the ink cartridge is replaced with a new one after the ink contained therein is used up, so it becomes necessary to make the ink in the ink reservoir flow to the pen tip anew. This makes the application of the water-based ink of the present invention even more useful. The ink cartridge may be one that also serves as a barrel that constitutes the writing instrument by connecting it to the writing instrument body, or one that covers and protects the barrel (rear barrel) after connecting it to the writing instrument body. In the latter case, in addition to application as an ink cartridge alone, it may be one in which the writing instrument body and the ink cartridge are connected in the writing instrument before use, or one that is stored in the barrel in a disconnected state so that the user can connect the ink cartridge in the barrel when using the writing instrument and start using it.

[0033] Furthermore, by using a transparent, colored transparent, or translucent molded body as the barrel, it is possible to check the ink color, the remaining amount of ink, etc. Furthermore, the barrel may be in the form of a ballpoint pen refill, with the refill housed within the outer barrel, or the barrel itself, with a tip attached to the tip, may serve as an ink container, with ink being filled directly into the barrel.

[0034] The ballpoint pen using the barrel can be either a cap type or a retractable type. As the retractable ballpoint pen, any type can be used as long as the writing tip provided on the ballpoint pen refill is stored in the outer barrel while being exposed to the outside air, and the writing tip protrudes from the outer barrel opening by the operation of the retractable mechanism. Examples of the method of operating the retractable mechanism include a knock type, a rotation type, and a slide type. The knock type has a knock portion at the rear end or side of the outer barrel, and pressing the knock portion causes the writing tip of the ballpoint pen refill to protrude and retract from the front end opening of the outer barrel, or a clip portion provided on the outer barrel is pressed to cause the writing tip of the ballpoint pen refill to protrude and retract from the front end opening of the outer barrel. The rotating type can be exemplified by a configuration in which the outer barrel has a rotating part (rear barrel, etc.), and the writing tip of the ballpoint pen refill appears and disappears from the front end opening of the outer barrel by rotating the rotating part. Examples of the sliding type include a configuration in which there is a sliding portion on the side of the barrel, and the writing tip of the ballpoint pen refill can be made to appear and disappear from the front end opening of the outer barrel by operating the sliding portion, or a configuration in which a clip portion provided on the outer barrel is slid to make the writing tip of the ballpoint pen refill appear and disappear from the front end opening of the outer barrel. The retractable ballpoint pen may be a composite type retractable ballpoint pen that accommodates a plurality of ballpoint pen refills in addition to the one that accommodates a single ballpoint pen refill in the outer barrel. The ink reservoir that constitutes the ballpoint pen refill may be made of resin or metal.

[0035] The rear end of the ink contained in the ballpoint pen refill can also be filled with an ink backflow prevention material. The ink backflow preventive material may be either liquid or solid. Examples of the liquid ink backflow preventive material include non-volatile media such as polybutene and silicone oil. If desired, silica, aluminum silicate, etc. may be added to the media. Furthermore, examples of solid ink backflow preventers include resin molded products. The liquid and solid ink backflow preventers can be used in combination. EXAMPLES

[0036] Examples will be described below, but the present invention is not limited to these examples. Table 1 shows the compositions and measured values ​​of the water-based inks for writing instruments of the Examples and Comparative Examples. The numerical values ​​of the compositions in the table show parts by mass. The viscosities of the inks of the Examples and Comparative Examples 1, 2, and 4 were measured at 20°C using a BL type rotational viscometer (manufactured by Toki Sangyo Co., Ltd.) at 50 rpm, and the viscosity of the ink of Comparative Example 3 was measured at a rotation speed of 30 rpm. The destabilization index (TSI) was measured by filling each ink composition into a glass bottle to a height of 40 mm or more, and using a liquid dispersion stability evaluation device "TURBISCAN" (manufactured by Formulaction) under the following measurement conditions so that the value of the entire sample was adopted regardless of the part: (Measuring device: dedicated glass bottle (inner diameter 25 mm x height 55 mm), measurement temperature: 40°C, measurement time: 168 hours, scan frequency: 5 minute intervals)

[0037] [Table 1]

[0038] [Table 2]

[0039] The contents of the ingredients in the table are explained according to the note numbers. (1) Self-dispersing pigment dispersion in which carbon black having carboxyl groups bonded to the surface by surface treatment is dispersed, 20% by mass dispersion in water, no dispersant contained, product name: Aqua-Black 162, manufactured by Tokai Carbon Co., Ltd. (2) Self-dispersing pigment dispersion in which carbon black having carboxyphenyl groups bonded to the surface by surface treatment is dispersed, 15% by mass water dispersion, no dispersant contained, product name: CAB-O-JET 300, manufactured by Cabot Specialty Chemicals (3) A resin-dispersed pigment dispersion obtained by adding 18% by mass of carbon black and 17% by mass of an anionic dispersant (Disparlon AQ-360, 30% active ingredient, manufactured by Kusumoto Chemicals Co., Ltd.) to 65% by mass of water and dispersing the mixture uniformly using a disperser. (4) A resin-dispersed pigment dispersion obtained by adding 15% by mass of carbon black and 7% by mass of a dispersant made of polyvinylpyrrolidone (Sokalan K-30P, 100% active ingredient, manufactured by BASF Japan) to 78% by mass of water and dispersing the mixture uniformly using a disperser. (5) A resin-dispersed pigment dispersion obtained by adding 20% ​​by mass of carbon black and 14% by mass of a dispersant made of a styrene-acrylic resin (JONCRYL 60J, 34% active ingredient, manufactured by BASF Japan Ltd.) to 66% by mass of water and dispersing the mixture uniformly using a disperser. (6) Product name: Plysurf AL, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (7) Product name: Proxel XL-2(S), manufactured by Arcsada Japan Co., Ltd. (8) MP Gokyo Food & Chemical Co., Ltd., product name: Monart Gum GS (9) Product name: Cellogen 5A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (10) Silicone-based defoaming agent, manufactured by Toray Dow Corning Co., Ltd., product name: FS Antifoam 013A (11) Polyether-based defoaming agent, manufactured by San Nopco Ltd., trade name: SN DEFOAMER 180

[0040] Preparation of ink for writing instruments The raw materials were mixed in the amounts described in the Examples and Comparative Examples, stirred and dissolved at 20° C. for 30 minutes, and then filtered to obtain a water-based ink composition for writing instruments.

[0041] Preparation of ballpoint pen A The ink compositions of Examples 1 to 6 and Comparative Examples 1 to 4 were directly placed inside the barrel, and a stainless steel cutting tip holding a 0.5 mm diameter cemented carbide ball with a comb-shaped ink flow rate adjusting member was attached, and then a cap was attached to prepare sample ballpoint pen A.

[0042] Making a marking pen The ink compositions of Examples 1 to 6 and Comparative Examples 1 to 4 were each impregnated into an ink occlusion body made of polyester sliver covered with a synthetic resin film, and housed in a barrel made of polypropylene resin. A resin-processed polyester fiber chip (bullet-shaped) was connected to the tip of the barrel via a holder, and then a cap was attached to produce a sample marking pen.

[0043] Ink cartridge production The inside of a bottomed cylindrical molded body made of polyethylene resin was used as an ink storage section, and 0.9 g of each of the ink compositions of Examples 1 to 4 and Examples 7 to 10 was filled therein. After that, a stopper was pressed into the inside of the opening to obtain an ink cartridge.

[0044] Preparation of ballpoint pen B The pen uses a pen core (formed by injection molding ABS resin material) with a stainless steel cutting tip at the tip that holds a 0.5 mm diameter cemented carbide ball, and the main body of the writing instrument is made by screwing the rear shaft, which can accommodate an ink cartridge, to the front shaft, which has a connection part (spear body) that allows the ink storage unit to be attached and detached (a cap is fitted). A sample ballpoint pen B was prepared by connecting the ink cartridge prepared above to the writing instrument body.

[0045] The following tests were carried out using the sample writing implements.

[0046] Ink Stability Test Each ink composition was placed in a 20 mL glass bottle, sealed, and then left for 60 days in an environment at 20° C. Thereafter, the state of the ink in the glass bottle was visually observed at room temperature.

[0047] Written exam After each sample ballpoint pen A and each sample marking pen were left in an environment of 20°C for 60 days, 12 spiral circles were handwritten in three consecutive lines on JIS P3201 writing paper A at room temperature. The state of the handwriting was then visually confirmed.

[0048] Handwritten Sensory Test Each sample ballpoint pen was used to handwrite 12 spiral circles in one line on JIS P3201 writing paper A. The writing feel was evaluated.

[0049] handwriting density The marks obtained in the writing test were visually observed and evaluated.

[0050] Cartridge replacement test After the sample ballpoint pen B was used at room temperature to continuously write a spiral circle on JIS P3201 writing paper A using a running tester (manufactured by Seiki Kogyo Kenkyusho Co., Ltd.), the ink cartridge was replaced with a new one with the same configuration, and the cap was removed and the pen tip was left facing downward for one hour. After that, the condition of the handwriting when 500 m was continuously written using the running tester was confirmed.

[0051] Ink discharge test After each sample ballpoint pen B that was confirmed to be writable was used to continuously write on JIS P3201 writing paper A at room temperature using the running test machine, the ink cartridge was then replaced with a new ink cartridge of the same configuration, and 12 spiral circles were continuously written on one line by hand on commercially available report paper at room temperature, and the condition of the handwriting was confirmed. The results of the above tests are shown in Tables 3 and 4 below.

[0052] [Table 3]

[0053] [Table 4]

[0054] The test results were evaluated as follows: Ink Stability Test ○: No abnormalities. ×: Precipitation is observed in the ink. Written exam ◯: Good dark writing is observed. △: There are some line skips in the handwriting. ×: The handwriting is smudged or broken, or writing is impossible. Handwritten Sensory Test ○: Very smooth. △: The writing feel is at a level that is not problematic for practical use. ×: Writing feels heavy. handwriting density ○: Shows thick and clear black writing. △: Black density is acceptable for practical use. ×: Feels thin as black. Cartridge replacement test ◯: The ink was supplied to the pen tip stably, and good handwriting was obtained without any smearing or skipping of lines. ×: Ink supply to the pen tip was irregular, and smudges and skipped lines were observed in the handwriting. Ink discharge test A: Good handwriting was observed. ×: Continuous, intermittent smudges or skipped lines were observed in the handwriting.

Claims

1. An aqueous ink composition for writing instruments comprising at least a self-dispersing pigment and a resin-dispersing pigment and water, wherein the amount of resin-dispersing pigment added is 1.5 to 12 times the amount of self-dispersing pigment.

2. The aqueous ink composition for writing instruments according to claim 1, comprising a nonionic dispersant or an anionic dispersant as a dispersant.

3. The aqueous ink composition for writing instruments according to claim 1, comprising a phosphate ester surfactant as a lubricant.

4. The aqueous ink composition for writing instruments according to claim 1, comprising an antifoaming agent.

5. The aqueous ink composition for writing instruments according to claim 4, comprising one or more defoaming agents selected from silicone-based, hydrophobic silica-based, polyether-based, acetylene glycol-based, acrylic polymer-based, oil-based, metal soap-based, and amide wax-based defoaming agents.

6. The aqueous ink composition for writing instruments according to claim 1, wherein the viscosity at 50 rpm measured by a rotational viscometer is in the range of 1 to 5 mPa·s (20°C).

7. A writing instrument containing the aqueous ink composition for writing instruments described in any one of claims 1 to 6.

8. An ink cartridge containing the aqueous ink composition for writing instruments described in any one of claims 1 to 6.