Aqueous ink composition for ballpoint pen

Abstract

This aqueous ink composition for a ballpoint pen contains at least a colorant, cellulose, a primary diol having 5 or more carbon atoms, and a secondary diol having 4 or fewer carbon atoms, wherein the ratio of the mass of the secondary diol to the mass of the primary diol is 1.3 to 35.0.

Description

Water-based ink composition for ballpoint pens

[0001] The present invention relates to a water-based ink composition for ballpoint pens.

[0002] In general, water-based ballpoint pens are characterized by a lighter writing feel than oil-based ballpoint pens and the ability to exude ink without rotating the ball, but they are known to have a unique problem of poorer drying properties of drawn lines than oil-based ballpoint pens, and various studies have been conducted to date.

[0003] Patent Document 1 discloses an ink composition containing carbon black and / or an organic pigment, water, a polysaccharide, two or more diols, and acrylic resin granules. The two or more diols include a first diol which is a diol having 5 to 7 carbon atoms and a second diol which is a diol having 1 to 4 carbon atoms, and the content of the first diol in the ink composition is 0.05% by weight or more. According to the invention related to Patent Document 1, it is disclosed that an ink composition capable of achieving both quick-drying property of ink and bleeding suppression can be provided. Further, Patent Document 1 discloses that the ratio of the content of the first diol to the content of the second diol (content of the first diol / content of the second diol) in the ink composition is preferably 1.5 or more and 5.0 or less.

[0004] Patent Document 2 discloses a water-based ink composition comprising at least a colorant and water, further containing 0.5 to 45% by weight of a polyhydric alcohol and / or glycol ethers which are soluble in water, have 4 or more carbon atoms, and have a specific gravity of less than 1.00 (25°C), and wherein the total amount of ink constituents having a specific gravity of 1.00 or more is 50% by weight or more in the ink, the water-based ink composition being for water-based ballpoint pens.

[0005] International Publication No. 2018 / 105151, Japanese Unexamined Patent Application Publication No. 2006-193688

[0006] According to Patent Document 1, an ink composition capable of achieving both quick-drying property of ink and bleeding suppression can be obtained. However, when the ink composition is used for a ballpoint pen, air bubbles may be drawn inward from the pen tip due to the rotation of the ball during writing.

[0007] The present invention provides a novel water-based ink composition for ballpoint pens that suppresses air bubbles from being trapped at the pen tip, ink dripping, streaking and bleed-through at the start of writing, and improves the drying speed of the drawn lines.

[0008] The present inventors, after diligent study, found that the above problems could be solved by the following means, and thus completed the present invention. That is, the present invention is as follows: <Aspect 1> An aqueous ink composition for ballpoint pens containing at least a colorant, cellulose, a primary diol having 5 or more carbon atoms, and a secondary diol having 4 or fewer carbon atoms, wherein the ratio of the mass of the secondary diol to the mass of the primary diol is 1.3 to 35.0. <Aspect 2> Temperature 25°C, shear rate 191.5 sec －１ A water-based ink composition for ballpoint pens having a viscosity value of 2 to 20 mPa·s. <Aspect 3> The water-based ink composition for ballpoint pens according to aspect 1 or 2, further containing an acrylic resin. <Aspect 4> The water-based ink composition for ballpoint pens according to any one of aspects 1 to 3, further containing a nonionic surfactant. <Aspect 5> The water-based ink composition for ballpoint pens according to any one of aspects 1 to 4, further containing a starch hydrolysate or a sugar alcohol. <Aspect 6> A ballpoint pen comprising at least an ink storage section, a writing section having a ball, and a holding section, wherein the water-based ink composition for ballpoint pens according to any one of aspects 1 to 5 is stored in the ink storage section. <Aspect 7> The ballpoint pen according to aspect 6, wherein the ink storage section is a hollow ink storage section. <Aspect 8> The ballpoint pen according to aspect 6 or 7, which is a retractable type.

[0009] According to the present invention, it is possible to provide a novel water-based ink composition for ballpoint pens that suppresses air bubbles from being drawn in from the pen tip, ink dripping, streaking and bleed-through at the start of writing, and improves the drying properties of the drawn lines.

[0010] 《Water-based ink composition for ballpoint pens》 The water-based ink composition for ballpoint pens of the present invention contains a colorant, cellulose, a primary diol having 5 or more carbon atoms, and a secondary diol having 4 or fewer carbon atoms, and the ratio of the mass of the secondary diol to the mass of the primary diol is 1.3 to 35.0.

[0011] In Patent Document 1, it was described that a combination of diols with 5 or more carbon atoms and diols with 4 or fewer carbon atoms was used to adjust the ink's penetration into writing materials such as paper and cloth within an appropriate range while maintaining the quick-drying properties of the liquid component of the ink. However, simply adjusting the mass ratio of these diols did not always yield sufficient performance. More specifically, when the content of diols with 5 or more carbon atoms was increased, while the inclusion of air bubbles from the pen tip became less likely, ink dripping from the pen tip and skipping at the start of writing became more likely. On the other hand, when the content of diols with 4 or fewer carbon atoms was increased, the opposite tendency was sometimes observed.

[0012] Furthermore, as described in Patent Document 1, when polysaccharides are simply added to increase viscosity, while the dripping of ink from the pen tip and the bleed-through when writing on paper are improved, air bubbles tend to be drawn into the pen tip, and the drying properties of the lines are impaired.

[0013] In response to this, the inventors have found that the above-mentioned problems can be solved by the above-mentioned configuration, particularly the above-mentioned mass ratio of the first and second diols, and the combination with cellulose. More specifically, with the above-mentioned mass ratio of the first and second diols, while ink dripping from the pen tip and skipping at the start of writing are suppressed, there is a tendency for air bubbles to be trapped from the pen tip. However, by adding cellulose, this trapping of air bubbles can be suppressed. Although we do not wish to be bound by theory, this is thought to be because the above-mentioned network of diols and cellulose makes it difficult for the ink film on the surface of the ball to break, and as a result, it becomes difficult for air bubble channels to be generated.

[0014] The ratio of the mass of the secondary diol to the mass of the primary diol is between 1.3 and 35.0. This ratio may be 1.3 or greater, 1.4 or greater, 1.5 or greater, 1.7 or greater, 2.0 or greater, 2.5 or greater, 3.0 or greater, or 3.3 or greater, and may also be 35.0 or less, 33.0 or less, 31.0 or less, 30.0 or less, 25.0 or less, 20.0 or less, 15.0 or less, 12.0 or less, 10.0 or less, 8.0 or less, or 7.0 or less.

[0015] The aqueous ink composition for ballpoint pens of the present invention, at a temperature of 25°C and a shear rate of 191.5 sec. －１ The viscosity value can be 2 mPa·s or more and 20 mPa·s or less. This viscosity may be 2 mPa·s or more, 3 mPa·s or more, 4 mPa·s or more, 5 mPa·s or more, 6 mPa·s or more, 7 mPa·s or more, or 8 mPa·s or more, and may also be 20 mPa·s or less, 18 mPa·s or less, 17 mPa·s or less, 16 mPa·s or less, 15 mPa·s or less, 14 mPa·s or less, or 13 mPa·s or less.

[0016] The static surface tension of the aqueous ink composition for ballpoint pens of the present invention may be, for example, 20 mN / m or more and 50 mN / m or less. This static surface tension may be 20 mN / m or more, 25 mN / m or more, 30 mN / m or more, 33 mN / m or more, 34 mN / m or more, 35 mN / m or more, or 37 mN / m or more, and may also be 50 mN / m or less, 47 mN / m or less, 45 mN / m or less, 43 mN / m or less, or 41 mN / m or less.

[0017] The static surface tension described above can be measured by the Wilhelmy method (plate method, using a platinum plate) under conditions of 25°C, 60% humidity, and atmospheric pressure (1 atm). For example, it can be measured using the "CBVP-Z" surface tension measuring device from Kyowa Interface Science Co., Ltd.

[0018] The aqueous ink composition for ballpoint pens of the present invention may further contain polysaccharides, acrylic resins, and surfactants. Furthermore, the aqueous ink composition for ballpoint pens of the present invention may further contain other components as optional.

[0019] The following describes each component of the present invention.

[0020] <Cellulose> Cellulose is contained in the aqueous ink composition for ballpoint pens of the present invention.

[0021] As cellulose, for example, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofibers, fermented cellulose, etc., can be used. As such cellulose, commercially available compositions, especially those commercially available as compositions containing polysaccharides, can be used.

[0022] The cellulose content may be 0.000003% by mass to 0.1% by mass relative to the mass of the aqueous ink composition for ballpoint pens. This content may be 0.000003% by mass or more, 0.000005% by mass or more, 0.00001% by mass or more, 0.00005% by mass or more, 0.0001% by mass or more, 0.0002% by mass or more, 0.0003% by mass or more, or 0.0004% by mass or more, and may also be 0.1% by mass or less, 0.05% by mass or less, 0.01% by mass or less, 0.005% by mass or less, 0.003% by mass or less, or 0.001% by mass or less.

[0023] <Polysaccharides> As polysaccharides, xanthan gum, dieutan gum, etc. can be used.

[0024] The polysaccharide content may be 0.000003% by mass to 0.003% by mass relative to the mass of the aqueous ink composition for ballpoint pens. This content may be 0.000003% by mass or more, 0.000005% by mass or more, 0.00001% by mass or more, 0.00005% by mass or more, 0.0001% by mass or more, 0.0002% by mass or more, 0.0003% by mass or more, or 0.0004% by mass or more, and is preferable from the viewpoint of suppressing ball entanglement to be 0.003% by mass or less, 0.001% by mass or less, 0.0007% by mass or less, or 0.0005% by mass or less.

[0025] <Aqueous media> Generally, aqueous media contain water and optional water-soluble organic solvents. In particular, in the present invention, the aqueous media contains at least water and the above-mentioned first and second diols.

[0026] Furthermore, the aqueous medium may further contain other water-soluble organic solvents other than the first and second diols mentioned above, but from the viewpoint of maximizing the effect of the above ratio of the first and second diols, it is preferable that the content is 5% by mass or less relative to the mass of the water-soluble ink composition for ballpoint pens, and in particular, that the water-soluble ink composition for ballpoint pens does not contain other water-soluble organic solvents. This content may be 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0% by mass.

[0027] In aqueous media, water has the highest liquid content, and in particular, the water content may be more than 50% by mass, 60% or more by mass, 70% or more by mass, 75% or more by mass, or 78% or more by mass, relative to the mass of the aqueous media, and may also be 100% or less by mass, 95% or less by mass, or 90% or less by mass.

[0028] Furthermore, the water content may be 50% by mass or more, 55% by mass or more, 60% by mass or more, or 63% by mass or more, relative to the mass of the water-based ink composition for ballpoint pens, and may also be 90% by mass or less, 85% by mass or less, 80% by mass or less, or 75% by mass or less.

[0029] (Water) For water, for example, tap water, purified water, distilled water, ion-exchanged water, pure water, etc. can be used.

[0030] (First Diol) A first diol is a diol with five or more carbon atoms.

[0031] Examples of primary diols that can be used include isoprene glycol (3-methyl-1,3-butanediol), 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, hexylene glycol, octylene glycol, and dipropylene glycol.

[0032] The content of the primary diol is not particularly limited as long as it satisfies the above ratio, and may be, for example, 5.0% or more by mass, 6.0% or more by mass, 7.0% or more by mass, 8.0% or more by mass, 9.0% or more by mass, 10.0% or more by mass, 11.0% or more by mass, 12.0% or more by mass, 13.0% or more by mass, or 14.0% or more by mass, based on the mass of the aqueous ink composition for ballpoint pens, or it may be 30.0% or less by mass, 27.0% or less by mass, 25.0% or less by mass, 22.0% or less by mass, 21.0% or less by mass, 20.0% or less by mass, 18.0% or less by mass, or 16.0% or less by mass.

[0033] (Secondary Diols) Secondary diols are diols with four or fewer carbon atoms.

[0034] As the secondary diol, ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 1,3-butanediol, etc., can be used.

[0035] The content of the secondary diol is not particularly limited as long as the above ratio is satisfied, and may be, for example, 0.1% by mass or more and 10.0% by mass or less based on the mass of the aqueous ink composition for ballpoint pens. This content may be 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, 1.0% by mass or more, 1.2% by mass or more, 1.5% by mass or more, 1.7% by mass or more, 2.0% by mass or more, 2.2% by mass or more, 2.5% by mass or more, or 2.7% by mass or more, and may also be 10.0% by mass or less, 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.5% by mass or less, 6.0% by mass or less, 5.0% by mass or less, 4.0% by mass or less, or 3.5% by mass or less.

[0036] (Other water-soluble organic solvents) Other water-soluble organic solvents that can be used include, for example, aromatics, alcohols, esters, and glycol ethers. These solvents may be used individually or in combination.

[0037] Examples of aromatic compounds that can be used include benzyl alcohol, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, propylene glycol monophenyl ether, diethylene glycol monophenyl ether, and alkylsulfonate phenyl esters.

[0038] Examples of alcohols that can be used include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, 1-pentanol, isoamyl alcohol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexanol, methylamyl alcohol, 2-ethylbutanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol, 2-octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, n-decanol, undecanol, n-decanol, trimethylnonyl alcohol, tetradecanol, heptadecanol, cyclohexanol, and 2-methylcyclohexanol.

[0039] Examples of esters include propylene glycol methyl ether acetate, propylene glycol diacetate, 3-methyl-3-methoxybutyl acetate, propylene glycol ethyl ether acetate, ethylene glycol ethyl ether acetate, butyl formate, isobutyl formate, isoamyl formate, propyl acetate, butyl acetate, isopropyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, isobutyl propionate, isoamyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, Methyl valerate, ethyl valerate, propyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, methyl trimethylacetate, ethyl trimethylacetate, propyl trimethylacetate, methyl caproate, ethyl caproate, propyl caproate, methyl caprylate, ethyl caprylate, propyl caprylate, methyl laurate, ethyl laurate, methyl oleate, ethyl oleate, caprylic triglyceride, tributyl citrate, octyl oxystearate, propylene glycol monolicinolate, methyl 2-hydroxyisobutyrate, 3-methoxybutyl acetate, etc. can be used.

[0040] Examples of glycol ethers that can be used include methyl glycol, isopropyl glycol, butyl glycol, butyl diglycol, butyl triglycol, isobutyl glycol, allyl glycol, methylpropylene glycol, methylpropylene diglycol, methylpropylene triglycol, propylpropylene glycol, propylpropylene diglycol, butylpropylene glycol, butylpropylene diglycol, methylpropylene glycol acetate, dimethyl glycol, dimethyl diglycol, dimethyl triglycol, diethyl diglycol, dimethylpropylene diglycol, and the like.

[0041] <Colorants> Various colorants that can be used in conventional inks can be used as colorants, such as dyes, pigments, or mixtures of dyes and pigments. These colorants may be used individually or in mixtures.

[0042] As the dye, any dye that dissolves or disperses in water can be used, and examples thereof include acid dyes such as eosin, phloxine, Water Yellow #6-C, Acid Red, Water Blue #105, Brilliant Blue FCF, and Nigrosine NB; direct dyes such as Direct Black 154, Direct Sky Blue 5B, and Violet BB; and basic dyes such as rhodamine and methyl violet.

[0043] As the pigment, conventionally known inorganic and organic pigments such as titanium oxide, resin particle pigments containing pigments or dyes, pseudo-pigments obtained by coloring resin emulsions with dyes or pigments, white plastic pigments, thermochromic pigments, photochromic particles and the like can be used without limitation.

[0044] Examples of the inorganic pigments that can be used include carbon black, titanium black, zinc oxide, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron oxide yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, chrome yellow, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine blue, precipitated barium sulfate, baryta powder, calcium carbonate, lead white, leaded white, Prussian blue, manganese violet, aluminum powder, brass powder, and the like.

[0045] Examples of organic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. Examples of such organic pigments include C.I. Pigment Blue 17, C.I. Pigment Blue 15, C.I. Pigment Blue 17, C.I. Pigment Blue 27, C.I. Pigment Red 5, C.I. Pigment Red 22, C.I. Pigment Red 38, C.I. Pigment Red 48, C.I. Pigment Red 49, C.I. Pigment Red 53, C.I. Pigment Red 57, C.I. Pigment Red 81, C.I. Pigment Red 104, C.I. Pigment Red 146, C.I. Pigment Red 245, C.I. Pigment Yellow 1, C.I. Pigment Yellow 3, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 17, C.I. Pigment Yellow 34, C.I. Pigment Yellow 55, C.I. Pigment Yellow 74, C.I. Pigment Yellow 95, C.I. Pigment Yellow 166, C.I. Pigment Yellow 167, C.I. Pigment Orange 5, C.I. Pigment Orange 13, C.I. Pigment Orange 16, C.I. Pigment Violet 1, C.I. Pigment Violet 3, C.I. Pigment Violet 19, C. Examples include I. Pigment Violet 23, C.I. Pigment Violet 50, and C.I. Pigment Green 7.

[0046] Examples of thermochromic pigments include thermochromic pigments produced by microencapsulating a thermochromic composition containing at least a leuco dye that functions as a color developer, a color developer that is a component capable of causing the leuco dye to develop color, and a color change temperature adjuster that can control the color change temperature in the color development of the leuco dye and the color developer, so that the composition has a predetermined D50 (for example, 0.1 to 6 μm). This D50 may be, for example, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.5 μm or more, 0.7 μm or more, or 0.9 μm or more, and may also be 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0047] As the photochromic particles, for example, photochromic particles composed of at least one or more selected from photochromic substances such as photochromic dyes (compounds) and fluorescent dyes, and a resin such as a terpene phenol resin can be used. Further, examples of the photochromic particles include photochromic particles produced by microencapsulating a photochromic composition containing at least one or more selected from photochromic substances such as photochromic dyes (compounds) and fluorescent dyes, an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers, so as to have a predetermined D50 (for example, 0.1 to 6 μm).

[0048] These photochromic particles can be made to have the property of being colorless in an indoor lighting environment (lighting equipment selected from indoor incandescent lamps, fluorescent lamps, lamps, white LEDs, etc.) and developing color in an ultraviolet irradiation environment (irradiation with a wavelength of 200 to 400 nm, or an irradiation environment with sunlight containing ultraviolet rays), by suitably using the above-mentioned photochromic substance.

[0049] In the present invention (including examples and the like), "D50" in principle means the median diameter (D50) calculated on a volume basis in the scattering intensity distribution measured by the dynamic light scattering method. It means the value of the median diameter (D50) calculated on a volume basis in the dynamic light scattering method. Exceptionally, for the D50 of particles that cannot be measured by the dynamic light scattering method, for example, particles having a D50 exceeding 5 μm, the D50 value obtained by any particle size measuring device known in the art, such as model: LA-960 (HORIBA, Ltd.), can be used. The shape of the particles blended in the water-based ink composition for ballpoint pens of the present invention may be spherical or non-spherical, and in either case, D50 can be measured using the above particle size measuring device.

[0050] Examples of microencapsulation methods for the above-mentioned thermochromic pigments and photochromic particles include interfacial polymerization, interfacial polycondensation, insitu polymerization, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion cooling, air suspension coating, and spray drying, which can be appropriately selected depending on the application.

[0051] For example, in a phase separation method from an aqueous solution, a thermochromic microcapsule pigment can be produced by a method including the following steps, particularly a method including the following steps in this order: (1) heating and melting a leuco dye, a developer, and a color change temperature regulator; (2) adding the heated and melted leuco dye, developer, and color change temperature regulator to an emulsifier solution, heating and stirring to disperse them into oil droplets to prepare a dispersion; (3) gradually adding a resin raw material capable of forming a wall film, such as a urethane resin, epoxy resin, or amino resin, for example, an amino resin solution, specifically an amino resin solution such as an aqueous solution of methylolmelamine, a urea solution, or a benzoguanamine solution, to the above dispersion, reacting the resin raw material to form a capsule film, thereby obtaining a thermochromic microcapsule pigment; and (4) filtering the dispersion containing the thermochromic microcapsule pigment.

[0052] In this thermochromic pigment, the color development temperature and decolorization temperature of each color can be set to a suitable temperature by appropriately combining the types and amounts of leuco dyes, developer agents, and color change temperature adjusters.

[0053] These colorants can be used individually or in mixtures of two or more. Furthermore, the D50 of these colorants, such as water-dispersible pigments, resin particle pigments, pseudo-pigments, white plastic pigments, multi-layer coated pigments, thermochromic pigments, and photochromic particles, varies depending on the ball diameter, ink composition, viscosity, etc., but a D50 of 0.02 to 6 μm is desirable. This D50 may be, for example, 0.02 μm or more, 0.05 μm or more, 0.07 μm or more, 0.10 μm or more, 0.20 μm or more, 0.30 μm or more, 0.50 μm or more, 0.70 μm or more, or 0.90 μm or more, and may also be 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0054] The content of these colorants can be appropriately increased or decreased depending on the ink line density, but may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, 0.9% by mass or more, or 1.0% by mass or more, relative to the total amount of the ink composition, and preferably 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0055] <Acrylic Resins> Acrylic resins are used as needed for purposes such as improving dispersibility, viscosity adjustment, and adhesion.

[0056] Examples of acrylic resins that can be used include ethyl acrylate, butyl acrylate, methyl acrylate, isobutyl methacrylate, isobornyl methacrylate, ethyl methacrylate, stearyl methacrylate, butyl methacrylate, methyl methacrylate, lauryl methacrylate, and cycloalkyl methacrylate, as well as copolymers thereof. These acrylic resins may be commercially available, for example, or obtained by known methods.

[0057] The acrylic resin may be in the form of a resin solution or a resin dispersion. When the acrylic resin is in the form of a resin dispersion, the D50 of the particles constituting the dispersion may be, for example, 0.01 to 0.25 μm. This D50 may be, for example, 0.01 μm or more, 0.03 μm or more, 0.05 μm or more, or 0.07 μm or more, and may also be 0.25 μm or less, 0.20 μm or less, 0.18 μm or less, 0.15 μm or less, 0.12 μm or less, or 0.10 μm or less.

[0058] The solid content of the acrylic resin may be 0.1% by mass or more and 20% by mass relative to the mass of the aqueous ink composition for ballpoint pens. This content may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, 2.0% by mass or more, 2.3% by mass or more, or 2.5% by mass or more, and may also be 20.0% by mass or less, 17.0% by mass or less, 15.0% by mass or less, 12.0% by mass or less, 10.0% by mass or less, 9.0% by mass or less, 8.5% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, or 4.5% by mass or less.

[0059] <Surfactants> Cationic surfactants, anionic surfactants, and nonionic surfactants can be used as surfactants, and among these, nonionic surfactants are preferred from the viewpoint of stability over time at high temperatures.

[0060] Examples of nonionic surfactants that can be used include fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, higher fatty acid esters of polyoxyalkylenes, alkyl phosphate esters, and acetylene-based surfactants.

[0061] From the viewpoint of long-term stability at high temperatures, it is preferable that the cloud point of nonionic surfactants be 80°C or higher. This cloud point may be 80°C or higher, 85°C or higher, 90°C or higher, 95°C or higher, or 100°C or higher. This cloud point can be measured by gradually increasing the temperature of an aqueous solution of the nonionic surfactant and measuring the temperature at which the solution becomes cloudy. This measurement can be performed using a known automatic cloud point tester, such as the AAP-6CP manufactured by Tanaka Scientific Instruments Co., Ltd.

[0062] The hydrophilic-lipophilic balance value (HLB value) of the surfactant may be between 13 and 20. The HLB value may be between 13 and 14 or 15, and may also be between 20 and 19, 18 and 17 or 16. Among these, an HLB value of 14 or higher is preferred from the viewpoint of the long-term stability of the water-based ink composition for ballpoint pens.

[0063] The surfactant content may be, for example, 0.1% by mass or more and 1.0% by mass or less, relative to the mass of the aqueous ink composition for ballpoint pens. This content may be 0.1% by mass or more, or 0.2% by mass or more, and may also be 1.0% by mass or less, 0.9% by mass or less, 0.8% by mass or less, 0.7% by mass or less, 0.6% by mass or less, or 0.5% by mass or less.

[0064] <Starch hydrolysates or sugar alcohols> Starch hydrolysates (dextrin) or sugar alcohols are starch hydrolysates with a DE value of 10 or more and 20 or less, or sugar alcohols obtained by reducing such starch hydrolysates. The DE value may be 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, or 15 or more, and may also be 20 or less, 19 or less, or 18 or less.

[0065] In this specification, the "DE (Dextrose Equivalent) value" is sometimes referred to as "dextrose equivalent," and is an index indicating the degree of decomposition when starch is broken down by acid or enzyme. It is known as a relative scale when the reducing power of dextrose (glucose) is set to 100. A DE value of 0 indicates starch, and the closer the value is to 0, the closer it is to starch. Conversely, the closer the DE value is to 100, the more advanced the hydrolysis of starch is. The DE value of dextrin can be measured by the Somogyi-Nelson method. For example, the DE values ​​of commercially available starch hydrolysates can be found in catalogs.

[0066] The starch hydrolysate may be a hydrolysate of corn starch (dent corn starch), waxy corn starch, sweet potato starch, potato starch, tapioca (cassava starch), wheat starch, and / or rice starch (glutinous rice starch or non-glutinous rice starch), and among these, a hydrolysate of tapioca is preferred from the viewpoint of suppressing skipping at the start of writing and suppressing ink dripping from the pen tip.

[0067] Such starch hydrolysates can be commercially available and possess the above-mentioned DE value.

[0068] As the sugar alcohol, a sugar alcohol obtained by reducing the starch hydrolysate described above, that is, a starch hydrolysate having the above DE value, can be used. Such a sugar alcohol can be one that is commercially available and has the above DE value before reduction. In other words, the DE value can be the value listed in the catalog as the DE value before reduction.

[0069] <Other Components> The aqueous ink composition for ballpoint pens of the present invention may contain other components as optional. Examples of other components include thickeners, humectants, dispersants, lubricants, pH adjusters, rust inhibitors, preservatives, and antibacterial agents.

[0070] As a thickening agent, thickening agents other than polysaccharides and starch hydrolysates, such as known alkali swelling association type thickening agents, can be used. However, from the viewpoint of suppressing air bubble entrapment from the pen tip, it is preferable that the content of such thickening agents be 0.0001% by mass or less, or 0.00005% by mass or less, relative to the mass of the aqueous ink composition for ballpoint pens of the present invention.

[0071] A water-soluble resin is used as the dispersant. Preferably, a water-soluble polymer is used as the dispersant.

[0072] As a lubricant, lubricants used in surface treatment agents for pigments can be used, such as nonionic surfactants like polyhydric alcohol fatty acid esters, sugar fatty acid esters, polyoxyalkylene fatty acid esters, and alkyl phosphate esters; anionic surfactants like phosphate esters, alkyl sulfonates of higher fatty acid amides, and alkyl allyl sulfonates; derivatives of polyalkylene glycols; and polyether-modified silicones.

[0073] Examples of pH adjusting agents include ammonia, urea, amines such as monoethanolamine, diethanolamine, and triethanolamine, alkali metal salts of carbonic acid and phosphoric acid such as sodium tripolyphosphate and sodium carbonate, and hydrates of alkali metal salts such as sodium hydroxide.

[0074] Furthermore, benzotriazole, toltriazole, dicyclohexylammonium nitride, saponins, etc., can be used as rust inhibitors. Phenol, sodium omazine, sodium benzoate, thiazoline compounds, benzimidazole compounds, etc., can be used as preservatives or antibacterial agents.

[0075] The other ingredients listed above may be used individually or in combination of two or more. Commercially available products containing these ingredients may also be used.

[0076] 《Ballpoint Pen》 The ballpoint pen of the present invention comprises at least an ink storage section, a writing section having a ball, and a holding section, wherein the above-mentioned aqueous ink composition for ballpoint pens is stored in the ink storage section.

[0077] The ink reservoir and the writing section may be integrated into a single unit. That is, the ballpoint pen of the present invention may have a refill having an ink reservoir and a writing section.

[0078] The ballpoint pen of the present invention may be a retractable ballpoint pen. A retractable ballpoint pen is generally a ballpoint pen having a retraction mechanism that allows the writing portion to be extended to the outside of the writing instrument and retracted into the writing instrument. The position of the retraction mechanism is not particularly limited and may be at the rear end of the writing portion, i.e., the end opposite to the writing portion, or it may be located on the side of the holder portion.

[0079] <Ink Storage Section> The ink storage section stores the above-mentioned water-based ink composition for ballpoint pens.

[0080] Any object capable of storing ink and supplying ink to the writing section can be used for the ink storage section. In particular, the water-based ink composition for ballpoint pens of the present invention is useful in that it can suppress ink dripping from the pen tip even when a hollow ink storage section is used.

[0081] <Writing section> The writing section may be a writing section having a ballpoint pen tip at its front.

[0082] A ballpoint pen tip may consist of a ball and a holder that rotatably holds the ball. The ball may be made of any material used for ballpoint pen balls, such as stainless steel, cemented carbide, or ceramics. The shape of the ballpoint pen tip is not particularly limited and may be, for example, bullet-shaped or needle-shaped.

[0083] Furthermore, from the viewpoint of writing quality, the surface roughness Ra of the ball is preferably less than 10 nm, 8 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, or 3 nm or less. This surface roughness may be 1.0 nm or more, 1.5 nm or more, or 1.7 nm or more.

[0084] In this invention (including the embodiments described later), the "surface roughness Ra" was measured using a non-contact surface shape measuring instrument (NewView 7200, Zygo Corporation) with a lens magnification of 50x, an evaluation length of 100 μm, and a Gaussian filter of 25 μm. All other conditions were met in accordance with JIS B0601 (Geometric specifications of products - surface properties).

[0085] From the viewpoint of writing performance, the ball clearance, that is, the distance the ball can move in the longitudinal axis direction of the ballpoint pen tip body, is preferably 30 μm or more, 40 μm or more, 50 μm or more, or 60 μm or more, and 120 μm or less, 110 μm or less, 100 μm or less, or 90 μm or less. This clearance can be measured by measuring the distance between the state in which the ball is in contact with the seat of the ballpoint pen tip and the state in which the ball is in contact with the crimped part at the tip of the ballpoint pen tip using a measuring microscope.

[0086] The present invention will be specifically described by examples and comparative examples, but the present invention is not limited thereto.

[0087] The substances shown in Table 1 were mixed in the amounts shown in Table 1 to obtain 100 parts by mass of an aqueous ballpoint pen ink composition.

[0088] The details of the substances shown in Table 1 are as follows: Lubricant: Phosphate ester (Phosphanol RD-510Y, Toho Chemical Industry Co., Ltd.) pH adjuster: Triethanolamine Dye: Red No. 105 Colored resin particles: Labcolor 224 (SMD) Black (black powder; Dainichi Seika Kogyo Co., Ltd., particle size 2-3 μm) Heat-changed particles: Heat-changed microcapsule pigment (blue powder, particle size 1.6 μm) CB: Black pigment (Carbon Black MCF-88, Mitsubishi Chemical Corporation) Cellulose composition A: Composition mainly composed of cellulose and further containing xanthan gum (Sun Artist H-PG, San-Ei Gen F.F.I. Co., Ltd.) Cellulose composition B: Composition mainly composed of cellulose and further containing xanthan gum (Sun Artist H-PN, San-Ei Gen F.F.I. Co., Ltd.) Acrylic A: Joncryl (registered trademark) 60J, BASF, solids content 34% Acrylic B: Joncryl PDX-7198, BASF, solids content 47.5% Acrylic C: Acrylic resin fine particle dispersion, FineSphere (registered trademark) FS-101, Nippon Paint Co., Ltd., solids content 20%, particle size 0.08 μm Acrylic D: Butyl methacrylate-cyclohexyl methacrylate copolymer emulsion, solids content 30% Nonionic A: Polyoxyethylene (POE)-based surfactant (Newpol PE-108, Sanyo Chemical Industries, Ltd., cloud point > 100°C, HLB 15.5) Nonionic B: POE polycyclic phenyl-based nonionic surfactant (Emulgen A90, Kao Corporation, cloud point 90°C, HLB 14.5) Sugar alcohol: Sugar alcohol obtained by reduction of tapioca-derived starch hydrolysate (H-PDX, Matsutani Chemical Industry Co., Ltd., DE value before reduction: 18) Starch: Tapioca-derived starch hydrolysate (Pinex #2, Matsutani Chemical Industry Co., Ltd., DE value: 11)

[0089] The viscosity of the obtained water-based ink composition for ballpoint pens was measured using an ELD viscometer at a temperature of 25°C and a shear rate of 191.5 sec. －１ The measurements were taken under the following conditions.

[0090] Furthermore, the static surface tension of the obtained aqueous ballpoint pen ink composition was measured using the Wilhelmy method with a platinum plate under conditions of 25°C, 60% humidity, and atmospheric pressure (1 atm).

[0091] 《Evaluation》 〈Air bubbles trapped from the pen tip〉 After writing 15 lines of 2cm diameter circles on copy paper over a length of 20cm, the pen was left with the tip facing downwards in an environment of 40°C and 60% humidity for one week. After returning to room temperature, the presence of air bubbles in the ink was visually checked. The evaluation criteria are as follows: A+: No air bubbles were present at all. A: One or two air bubbles were present. B: Air bubbles were scattered. C: A large number of air bubbles were present.

[0092] <Ink dripping from the pen tip> The pen tip was left facing downwards for one hour in an environment with a temperature of 25°C and humidity of 60%. Afterwards, the size of the ink droplets that accumulated on the pen tip was evaluated. A+: No ink droplets were observed. A: The size of the ink droplet was less than half the diameter of the ball. B: The size of the ink droplet was more than half the diameter of the ball but less than or equal to the diameter of the ball. C: The size of the ink droplet exceeded the diameter of the ball.

[0093] <Suppression of smudging at the start of writing> Circles with a diameter of 2 cm were drawn on copy paper, and smudging from the start of writing was evaluated. A+: No smudging occurred at all. A: The lines appeared slightly lighter in density than the A+ lines, but no smudging occurred at all. B: Smudging occurred, but the lines were still clearly recognizable. C: Smudging occurred to a degree that significantly affected the recognition of the lines.

[0094] <Drying properties of the lines> After drawing a 5 cm long straight line on copy paper, the ink staining on the fingers and the staining of the lines were evaluated when the lines were rubbed with a finger after 10 seconds. The evaluation criteria are as follows: A+: No transfer marks remained even when rubbed 1 second after writing. A: No transfer marks remained even when rubbed 2-3 seconds after writing. B: No transfer marks remained between 4-5 seconds after writing. C: No transfer marks remained until more than 5 seconds after writing.

[0095] <Ink bleed-through when writing on paper> After drawing a 5cm long straight line on copy paper, the ink bleed-through was evaluated by observing the back side. The evaluation criteria are as follows: A+: No bleed-through at all. A: There were some areas where the color was slightly darker, but there was almost no bleed-through. B: The color was slightly darker overall. C: The darkness of the lines appeared to be the same as the front side.

[0096] The configurations and evaluation results of the examples and comparative examples are shown in Tables 1 and 2.

[0097]

[0098]

[0099] From Table 1, it can be seen that the water-based ink compositions for ballpoint pens in the examples have been improved to suppress air bubbles from being trapped at the pen tip, ink dripping, streaking at the start of writing, and bleed-through, and also have good drying properties for the lines drawn.

Claims

1. An aqueous ink composition for ballpoint pens, comprising a colorant, cellulose, a primary diol having 5 or more carbon atoms, and a secondary diol having 4 or fewer carbon atoms, wherein the ratio of the mass of the secondary diol to the mass of the primary diol is 1.3 to 35.

0.

2. Temperature 25℃, shear rate 191.5sec －１ A water-based ink composition for ballpoint pens having a viscosity value of 2 to 20 mPa·s.

3. The aqueous ink composition for ballpoint pens according to claim 1 or 2, further comprising an acrylic resin.

4. The aqueous ink composition for ballpoint pens according to any one of claims 1 to 3, further comprising a nonionic surfactant.

5. The aqueous ink composition for ballpoint pens according to any one of claims 1 to 4, further comprising a starch hydrolysate or a sugar alcohol.

6. A ballpoint pen comprising at least an ink storage section, a writing section having a ball, and a holding section, wherein the water-based ink composition for ballpoint pens described in any one of claims 1 to 5 is stored in the ink storage section.

7. The ballpoint pen according to claim 6, wherein the ink storage section is a hollow ink storage section.

8. The ballpoint pen according to claim 6 or 7, which is a retractable type.

Images