Water-based ink composition for ballpoint pens

Abstract

The present invention provides an aqueous ink composition for ballpoint pens that can suppress wear of the ballpoint pen tip while using a hard inorganic pigment. [Solution] The water-based ink composition for ballpoint pens of the present invention, It contains at least resin particles and an inorganic pigment composed of an inorganic compound having a Mohs hardness of 5.5 or higher. The ratio of the average particle diameter of the resin particles to the average particle diameter of the inorganic pigment is 2.0 or greater, and The average particle size of the resin particles and the inorganic pigment is the volume-average particle size Mv obtained from the scattering intensity distribution measured by laser diffraction.

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition for ballpoint pens.

Background Art

[0002] Conventionally, it has been well known to incorporate titanium oxide into an aqueous ink composition for writing instruments for the purpose of imparting concealment to the writing strokes or for the purpose of achieving a pastel tone. However, due to the large specific gravity of titanium oxide, it is difficult to maintain a stable dispersion state, leading to various restrictions in the design of the ink. To satisfy these restrictions, various proposals have been made.

[0003] In Patent Document 1, an aqueous white ink composition for ballpoint pens is disclosed, which comprises, as essential components, a microcapsule pigment encapsulating titanium oxide, water, and a water-soluble organic solvent.

[0004] In Patent Document 2, an aqueous ink composition for writing instruments is disclosed, which comprises at least a pigment (a) and colored resin particles (A) encapsulating the pigment (a).

[0005] In Patent Document 3, an aqueous ink composition for ballpoint pens is disclosed, which comprises at least 1 to 35% by mass of titanium oxide having an average particle diameter exceeding 0.1 μm and not exceeding 1 μm and 1 to 35% by mass of non-adhesive urethane-based particles having an average particle diameter of 0.1 μm or more and 6 μm or less.

[0006] In Patent Document 4, an aqueous ink composition for writing instruments is disclosed, which comprises at least titanium oxide and a microcapsule pigment encapsulating a fluorescent whitening agent.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

[0008] When hard inorganic pigments such as titanium dioxide were incorporated into the ink composition without being encapsulated in resin, and this was used in a ballpoint pen, the ballpoint pen tip sometimes became prone to wear.

[0009] Therefore, the present invention provides an aqueous ink composition for ballpoint pens that can suppress wear of the ballpoint pen tip while using a hard inorganic pigment. [Means for solving the problem]

[0010] The inventors, after diligent research, discovered 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> Contains at least resin particles and an inorganic pigment composed of an inorganic compound having a Mohs hardness of 5.5 or higher. The ratio of the average particle diameter of the resin particles to the average particle diameter of the inorganic pigment is 2.0 or greater, and The average particle size of the resin particles and the inorganic pigment is the volume-average particle size Mv obtained from the scattering intensity distribution measured by laser diffraction. A water-based ink composition for ballpoint pens. <Aspect 2> The aqueous ink composition for ballpoint pens according to aspect 1, wherein at least a portion of the resin particles contains an inorganic pigment. <Aspect 3> The aqueous ink composition for ballpoint pens according to aspect 1 or 2, wherein the resin constituting the resin particles is at least one selected from the group consisting of urethane resin, urea resin, urea / urethane resin, melamine resin, acrylic resin, and olefin resin. <Aspect 4> An aqueous ink composition for ballpoint pens according to any one of aspects 1 to 3, further containing hollow resin particles. <Aspect 5> The aqueous ink composition for ballpoint pens according to any one of aspects 1 to 4, wherein the ratio of the circularity of the resin particles to the circularity of the inorganic pigment is 1.2 or more. <Pattern 6> Temperature 25°C, shear rate 3.8s -1 An aqueous ink composition for ballpoint pens according to any one of embodiments 1 to 5, wherein the viscosity measured under the specified conditions is 300 to 3000 mPa·s. <Aspect 7> A ballpoint pen having the aqueous ink composition for ballpoint pens described in any one of aspects 1 to 6. <Aspect 8> The ballpoint pen according to aspect 7, wherein the ball diameter is 0.7 mm or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an aqueous ink composition for ballpoint pens that can suppress wear of the ballpoint pen tip even when a hard inorganic pigment is used. [Modes for carrying out the invention]

[0012] Water-based ink composition for ballpoint pens The present invention provides an aqueous ink composition for ballpoint pens. It contains at least resin particles and an inorganic pigment composed of an inorganic compound having a Mohs hardness of 5.5 or higher. The ratio of the average particle diameter of the resin particles to the average particle diameter of the inorganic pigment is 2.0 or greater, and The average particle size of the resin particles and the inorganic pigment is the volume-average particle size Mv obtained from the scattering intensity distribution measured by laser diffraction.

[0013] The inventors have found that even when using the above inorganic pigments, wear of the ballpoint pen tip can be suppressed by using resin particles having an average particle diameter three times or more that of the above inorganic pigments in combination. Without wishing to be bound by theory, this is presumably because when the ball rotates during writing with a ballpoint pen, the above resin particles enter the flow path between the ballpoint pen tip and the ball, thereby suppressing contact between the inorganic pigment and the ballpoint pen tip.

[0014] In the present invention, "average particle diameter" means the volume average particle diameter Mv obtained in the scattering intensity distribution measured by the laser diffraction method, that is, the average particle diameter weighted by volume. Measurement of the volume average particle diameter can be performed using a particle size analyzer [Microtrac HRA9320-X100 (Nikkiso Co., Ltd.)].

[0015] In this specification, "aqueous ink composition" means an ink composition containing an aqueous medium as a liquid component.

[0016] The ratio of the average particle diameter of the resin particles to the average particle diameter of the inorganic pigment is 2.0 or more. This ratio may be 2.0 or more, 3.0 or more, 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, or 9.0 or more, and may also be 20.0 or less, 17.0 or less, 15.0 or less, 13.0 or less, 12.0 or less, or 11.0 or less.

[0017] From the viewpoint of suppressing wear of the ballpoint pen tip, it is preferable that the ratio of the circularity of the resin particles to the circularity of the inorganic pigment is 1.1 or more. This ratio may be 1.1 or more, or 1.2 or more, and may also be 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, or 1.3 or less.

[0018] In this specification, circularity is the average value of 500 particles measured by the image analysis method, and can be measured using, for example, Mac-View of Mountech Co., Ltd.

[0019] This circularity is calculated as (4π × area of ​​microspheres on the image) / (perimeter of microspheres on the image). 2 It can be calculated using the following formula. The circularity calculated using this formula approaches 1 as the shape of the particle on the image approaches a perfect circle, and when the shape of the particle on the image is a perfect circle, the circularity is 1.

[0020] The aqueous ink composition for ballpoint pens of the present invention, at a temperature of 25°C and a shear rate of 3.8 s. -1 The viscosity measured under these conditions may be 300 to 3000 mPa·s. This viscosity may be 300 mPa·s or more, 400 mPa·s or more, 500 mPa·s or more, or 550 mPa·s or more, and may also be 3000 mPa·s or less, 2800 mPa·s or less, 2500 mPa·s or less, 2200 mPa·s or less, 2000 mPa·s or less, 1800 mPa·s or less, 1500 mPa·s or less, 1200 mPa·s or less, or 1100 mPa·s or less.

[0021] In another embodiment, the aqueous ink composition for ballpoint pens of the present invention, It contains at least a first resin particle, a second resin particle, and an inorganic pigment composed of an inorganic compound having a Mohs hardness of 5.5 or higher. The ratio of the average particle diameter of the first resin particles to the average particle diameter of the inorganic pigment is 2.0 or more, and The ratio of the average particle diameter of the second resin particles to the average particle diameter of the inorganic pigment may be less than 2.0.

[0022] In another embodiment, the first resin particles may be inorganic pigments, in particular inorganic pigments composed of inorganic compounds having a Mohs hardness of 5.5 or higher, and in particular inorganic pigments composed of inorganic compounds of the same type as the above-mentioned inorganic pigments, and the second resin particles may be hollow resin particles.

[0023] The aqueous ink composition for writing instruments of the present invention may further contain other colorants as optional. Furthermore, the aqueous ink composition for writing instruments of the present invention may further contain other components as optional.

[0024] The following describes each component of the present invention.

[0025] <Aqueous medium> The aqueous medium contains water and an optional water-soluble organic solvent. In the aqueous medium, water has the highest liquid content, and the water content may be 30% by mass or more, 40% by mass or more, 50% by mass or more, more than 50% by mass, 60% by mass or more, 70% by mass or more, 75% by mass or more, or 78% by mass or more, relative to the mass of the aqueous medium, and may also be 100% by mass or less, 95% by mass or less, or 90% by mass or less.

[0026] (water) For water, for example, tap water, purified water, distilled water, ion-exchanged water, pure water, etc., can be used.

[0027] (Water-soluble organic solvent) As water-soluble organic solvents, for example, aromatics, alcohols, polyhydric alcohols, ethers, esters, etc., can be used, and among these, polyhydric alcohols are preferred from the viewpoint of writing properties. These solvents may be used individually or in combination.

[0028] 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.

[0029] 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.

[0030] Examples of polyhydric alcohols that can be used include dihydric alcohols such as ethylene glycol, propylene glycol, 3-methyl-1,3-butanediol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, hexylene glycol, and octylene glycol, as well as trihydric alcohols such as glycerin.

[0031] Examples of ethers that can be used include methyl isopropyl ether, ethyl ether, ethyl propyl ether, ethyl butyl ether, isopropyl ether, butyl ether, hexyl ether, 2-ethylhexyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethyl butyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, 3-methyl-3-methoxy-1-butanol, 3-methoxy-1-butanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol-t-butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and tetrapropylene glycol monobutyl ether.

[0032] 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 acid triglyceride, tributyl citrate, octyl oxystearate, propylene glycol monolicinolate, methyl 2-hydroxyisobutyrate, 3-methoxybutyl acetate, etc. can be used.

[0033] The content of the water-soluble organic solvent may be 3% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more, or 12% by mass or more, based on the total mass of the water-based ink composition for ballpoint pens, and may also be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 17% by mass or less.

[0034] <First resin particle> The first resin particles are contained in the aqueous ink composition for ballpoint pens of the present invention.

[0035] The ratio of the average particle size of the first resin particles to the average particle size of the inorganic pigment is 2.0 or greater. This ratio may be 2.0 or greater, 3.0 or greater, 5.0 or greater, 6.0 or greater, 7.0 or greater, 8.0 or greater, or 9.0 or greater, and may also be 20.0 or less, 17.0 or less, 15.0 or less, 13.0 or less, 12.0 or less, or 11.0 or less.

[0036] The average particle size of the first resin particles is not particularly limited as long as the above ratio is satisfied, and may be, for example, 1.0 μm or more and 5.0 μm or less. This particle size may be 1.2 μm or more, 1.5 μm or more, 1.7 μm or more, 1.8 μm or more, or 1.9 μm or more, and may also be 5.0 μm or less, 4.5 μm or less, 4.0 μm or less, 3.5 μm or less, 3.0 μm or less, 2.5 μm or less, 2.2 μm or less, or 2.1 μm or less.

[0037] The first resin particles may be composed of a thermoplastic resin having a Mohs hardness of 4.5 or less. This Mohs hardness may be 4.5 or less, 4.0 or less, or 3.8 or less, and may also be 2.0 or more, 2.5 or more, 3.0 or more, or 3.3 or more.

[0038] The resin constituting the first resin particles may be urethane resin, urea resin, urea / urethane resin, melamine resin, acrylic resin, or olefin resin. These resins may be used individually or in mixtures.

[0039] The first resin particles may be resin particles containing an inorganic pigment, particularly an inorganic pigment composed of an inorganic compound having a Mohs hardness of 5.5 or higher, or an inorganic pigment composed of the same type of inorganic compound as the inorganic pigments described below, or they may be solid or hollow resin particles. These embodiments of resin particles may be used individually or in combination.

[0040] The circularity of the resin particles can be 0.60 or higher, 0.70 or higher, 0.80 or higher, or 0.85 or higher, and can also be 1.00 or lower, 0.98 or lower, or 0.95 or lower.

[0041] The content of the first resin particles may be 1% by mass or more and 30% by mass or less, relative to the mass of the water-based ink composition for ballpoint pens. This content may be 1% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more, 12% by mass or more, or 14% by mass or more, and may also be 30% by mass or less, 25% by mass or less, 22% by mass or less, 20% by mass or less, 18% by mass or less, or 16% by mass or less.

[0042] <First resin particle: A particle containing an inorganic pigment> Resin particles containing inorganic pigments can be manufactured by microencapsulating a composition containing at least the same type of inorganic pigment as described below, to a predetermined particle size, specifically by encapsulating it in a shell layer (shell body) composed of a wall-forming material (wall material).

[0043] Examples of microencapsulation methods 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.

[0044] The shell layer can be prepared, for example, by (1) dispersing at least one monomer component of a resin that forms the shell layer with an inorganic pigment and performing interfacial polymerization, or by (2) an emulsification step of dispersing an oily component (oil phase) in an aqueous solvent (aqueous phase) to prepare an emulsion, and an interfacial polymerization step of adding at least one of an amine component and an alcohol component to the emulsion and performing interfacial polymerization.

[0045] More specifically, resin particles containing inorganic pigments can be manufactured by the method described in Patent Document 2.

[0046] The ratio of the mass of resin particles containing inorganic pigment to the mass of inorganic pigment may be 1.0 or more and 5.0 or less. This ratio may be 1.0 or more, 1.2 or more, 1.3 or more, or 1.4 or more, and may also be 5.0 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.0 or less, 1.8 or less, or 1.6 or less.

[0047] Any inorganic pigment can be used as the inorganic pigment. That is, the inorganic pigment to be embedded in the resin particles may be an inorganic pigment composed of an inorganic compound with a Mohs hardness of 5.5 or higher, in particular an inorganic pigment composed of the same type of inorganic compound as the inorganic pigments listed below, or it may be composed of an inorganic compound with a Mohs hardness of less than 5.5.

[0048] Inorganic pigments composed of inorganic compounds with a Mohs hardness of 5.5 or higher include, for example, iron oxides such as iron black, red iron oxide, and iron yellow (Mohs hardness 6.0), titanium dioxide (Mohs hardness 6.5), chromium oxide (Mohs hardness 8.0-9.0), viridian (Mohs hardness 7.5-8.0), and white carbon (Mohs hardness 7.0).

[0049] Inorganic pigments composed of inorganic compounds with a Mohs hardness of less than 5.5 include aluminum (Mohs hardness 2.0-3.0), zinc sulfide (Mohs hardness 3.5-4.0), zinc oxide (Mohs hardness 2.5), cadmium yellow (Mohs hardness 3.0-3.5), cadmium red (Mohs hardness 3.0-3.5), lithopone (Mohs hardness 3.0), molybdide orange (Mohs hardness 3.0), clay (Mohs hardness 1.0-3.0), talc (Mohs hardness 1.0), ultramarine (Mohs hardness 4.0), barium sulfate (Mohs hardness 3.0-3.5), barite (Mohs hardness 3.0-3.5), calcium carbonate (Mohs hardness 4.0), and brass (Mohs hardness 3.0-4.0).

[0050] The inorganic pigment content in the resin particles may be, for example, 10 to 70% by mass. This content may be 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, or 33% by mass or more, and may also be 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, or 38% by mass or less.

[0051] <First resin particle: Solid or hollow resin particle> The solid or hollow resin particles may be solid or hollow resin particles composed of the above-mentioned resin. Commercially available solid or hollow resin particles can be used as such solid or hollow resin particles. When these resin particles are used as at least a part of the first resin particles, it is preferable to use hollow resin particles from the viewpoint of color development.

[0052] <Inorganic pigments> Inorganic pigments are contained in the aqueous ink composition for ballpoint pens of the present invention.

[0053] Inorganic pigments are composed of inorganic compounds having a Mohs hardness of 5.5 or higher. This Mohs hardness may be 5.5 or higher, or 5.8 or higher, and may also be 8.0 or lower, 7.5 or lower, 7.0 or lower, or 6.8 or lower.

[0054] Such inorganic pigments include those composed of inorganic compounds with a Mohs hardness of 5.5 or higher, as mentioned above for resin particles, such as iron oxides like iron black, red iron oxide, and iron yellow, titanium dioxide, chromium oxide, viridian, and white carbon.

[0055] The average particle size of the inorganic pigment may be 0.01 μm or more and 1.0 μm or less. This average particle size may be 0.01 μm or more, 0.03 μm or more, 0.05 μm or more, 0.07 μm or more, 0.10 μm or more, 0.15 μm or more, or 0.18 μm or more, and may also be 1.0 μm or less, 0.8 μm or less, 0.6 μm or less, 0.5 μm or less, 0.4 μm or less, or 0.3 μm or less.

[0056] The circularity of the inorganic pigment can be 0.50 or higher, 0.60 or higher, or 0.65 or higher, and can also be 0.80 or lower, or 0.75 or lower.

[0057] <Second resin particles> The second resin particles may be contained in the water-based ink composition for ballpoint pens.

[0058] The material constituting the second resin particles and the morphology of the second resin particles can be described by referring to the description of the first resin particles. In particular, in embodiments in which resin particles containing inorganic particles are included as the first resin particles, the color development can be further improved by further including hollow resin particles as the second resin particles.

[0059] The ratio of the average particle size of the second resin particles to the average particle size of the inorganic pigment is less than 2.0. This ratio may be less than 2.0, 1.5 or less, or 1.2 or less, and may be 0.1 or more, 0.3 or more, 0.5 or more, 0.7 or more, or 0.9 or more.

[0060] The average particle diameter of the second resin particles is not particularly limited as long as the above ratio is satisfied, and may be, for example, 0.01 μm or more and 1.0 μm or less. This average particle diameter may be 0.01 μm or more, 0.03 μm or more, 0.05 μm or more, 0.07 μm or more, 0.10 μm or more, 0.15 μm or more, or 0.18 μm or more, and may also be 1.0 μm or less, 0.8 μm or less, 0.6 μm or less, 0.5 μm or less, 0.4 μm or less, or 0.3 μm or less.

[0061] The content of the second resin particles may be 1% by mass or more and 15% by mass or less, relative to the mass of the water-based ink composition for ballpoint pens. This content may be 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more, and may also be 15% by mass or less, 13% by mass or less, 10% by mass or less, 8% by mass or less, 7% by mass or less, or 6% by mass or less.

[0062] <Other colorants> Other colorants that can be used in conventional inks include dyes, pigments, or mixtures of dyes and pigments. These colorants may be used individually or in combination.

[0063] As dyes, all dyes that dissolve or disperse in water can be used, including, for example, acid dyes such as eosin, foxine, 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.

[0064] As pigments, inorganic pigments other than the inorganic pigments mentioned above, organic pigments, etc., can be used without restriction.

[0065] Inorganic pigments other than those listed above, i.e., inorganic compounds with a Mohs hardness of less than 5.5, include aluminum, zinc sulfide, zinc oxide, cadmium yellow, cadmium red, lithopone, molybdide orange, clay, talc, ultramarine, barium sulfate, barite, calcium carbonate, brass, and the like.

[0066] 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 CI Pigment Blue 17, CI Pigment Blue 15, CI Pigment Blue 17, CI Pigment Blue 27, CI Pigment Red 5, CI Pigment Red 22, CI Pigment Red 38, CI Pigment Red 48, CI Pigment Red 49, CI Pigment Red 53, CI Pigment Red 57, CI Pigment Red 81, CI Pigment Red 104, CI Pigment Red 146, CI Pigment Red 245, CI Pigment Yellow 1, CI Pigment Yellow 3, CI Pigment Yellow 12, and CI Pigment Examples include CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Yellow 34, CI Pigment Yellow 55, CI Pigment Yellow 74, CI Pigment Yellow 95, CI Pigment Yellow 166, CI Pigment Yellow 167, CI Pigment Orange 5, CI Pigment Orange 13, CI Pigment Orange 16, CI Pigment Violet 1, CI Pigment Violet 3, CI Pigment Violet 19, CI Pigment Violet 23, CI Pigment Violet 50, CI Pigment Green 7, etc.

[0067] These colorants can be used individually or in mixtures of two or more. Furthermore, the average particle size of these colorants, such as water-dispersible pigments, pseudo-pigments, white plastic pigments, and multi-layer coated pigments, varies depending on the ball diameter, ink composition, viscosity, etc., but an average particle size of 0.02 to 6 μm is desirable. This average particle size 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.

[0068] 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.

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

[0070] As a thickening agent, it is preferable to use polysaccharides such as xanthan gum or dieutan gum, from the viewpoint of suppressing pigment sedimentation without excessively increasing viscosity.

[0071] As a viscosity modifier, at least one selected from the group consisting of, for example, polysaccharides and synthetic polymers is preferable. Among these, the use of polysaccharides is preferable from the viewpoint of suppressing the sedimentation of inorganic pigments without excessively increasing viscosity.

[0072] Examples of polysaccharides include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, gellan gum, succinoglycan, dieutan gum, dextran, starch glycolic acid and its salts, and cellulose derivatives.

[0073] Examples of synthetic polymers include crosslinked acrylic acid polymers and their salts, non-crosslinked acrylic acid polymers and their salts, associated viscoelastic modifiers such as styrene acrylic acid copolymers and their salts, propylene glycol alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, carboxyvinyl polymer, polyethylene hydroxide, and copolymers of vinyl acetate and polyvinylpyrrolidone.

[0074] The content of the thickener may be, for example, 0.01% by mass or more and 2.00% by mass or less, relative to the mass of the aqueous ink composition for writing instruments. This content may be 0.01% by mass or more, 0.03% by mass or more, 0.05% by mass or more, 0.10% by mass or more, or 0.15% by mass or more, and may also be 2.00% by mass or less, 1.50% by mass or less, 1.20% by mass or less, 1.00% by mass or less, 0.70% by mass or less, 0.50% by mass or less, 0.30% by mass or less, or 0.25% by mass or less.

[0075] A water-soluble resin is used as the dispersant. Preferably, a water-soluble polymer is used as the dispersant.

[0076] As a lubricant, lubricants used in surface treatment agents for pigments can be used. For example, nonionic surfactants such as 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 can be used, as well as anionic surfactants such as phosphate esters, alkyl sulfonates of higher fatty acid amides, and alkyl allyl sulfonates, and derivatives of polyalkylene glycols and polyether-modified silicones can be used.

[0077] Examples of pH adjusters 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.

[0078] 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.

[0079] The bonding resin is used, if necessary, for viscosity adjustment and to improve bonding strength. Examples of bonding resins include water-soluble resins and resin emulsions.

[0080] As water-soluble resins, for example, water-soluble resins having hydrophobic parts within the molecule can be used, such as polyacrylic acid, water-soluble styrene-acrylic resin, water-soluble styrene-maleic acid resin, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble maleic acid resin, water-soluble styrene resin, water-soluble ester-acrylic resin, ethylene-maleic acid copolymer, polyethylene oxide, and water-soluble urethane resin.

[0081] As the resin emulsion, at least one selected from, for example, polyolefin emulsions, acrylic emulsions, vinyl acetate emulsions, urethane emulsions, styrene-butadiene emulsions, and styrene-acrylonitrile emulsions can be used.

[0082] The bonding resin may be used alone or in mixtures. In particular, from the viewpoint of bonding performance, it is preferable to use one or more types of the above-mentioned water-soluble resin and resin emulsion, i.e., a total of two or more types of bonding resins.

[0083] 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.

[0084] Ballpoint pen The ballpoint pen of the present invention has the above-described aqueous ink composition for ballpoint pens. The ballpoint pen of the present invention may include an ink storage section, a writing section, and a holding section. The above-described aqueous ink composition for ballpoint pens may be stored in the ink storage section.

[0085] 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.

[0086] 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 part to be extended to the outside of the ballpoint pen and retracted into the inside of the ballpoint pen. The position of the retraction mechanism is not particularly limited and may be at the rear end of the writing part, i.e., the end opposite to the writing part, or it may be located on the side of the holding part.

[0087] <Ink storage section> The ink storage section contains the above-mentioned water-based ink composition for ballpoint pens.

[0088] 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.

[0089] <Writing Department> The writing section may be a writing section having a ballpoint pen tip at its front.

[0090] The ballpoint pen tip may consist of a ball and a holder that rotatably holds the ball. The shape of the ballpoint pen tip is not particularly limited and may be, for example, bullet-shaped or needle-shaped.

[0091] The ball may be made of any material used for ballpoint pen balls, such as cemented carbide. The holder may be made of stainless steel. In particular, holders made of stainless steel are susceptible to the effects of inorganic pigments with a Mohs hardness of 5.5 or higher, so the aqueous ink composition for ballpoint pens of the present invention is useful when such a holder is present.

[0092] Furthermore, the ballpoint pen tip may have a spring to bias the ball toward the tip. The spring may be nickel (Ni) plated on its surface.

[0093] Furthermore, from the viewpoint of writing feel, 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.

[0094] The ball diameter may be, for example, 0.1 mm or more and 0.7 mm or less. This diameter may be 0.7 mm or less, 0.6 mm or less, 0.5 mm or less, 0.4 mm or less, or less than 0.4 mm, and may also be 0.1 mm or more, 0.2 mm or more, or 0.3 mm or more. In particular, when the ball diameter is 0.4 mm or less or less than 0.4 mm, the ball clearance tends to become narrower, and as a result, the ball pen tip becomes more susceptible to wear, so the aqueous ink composition for ballpoint pens of the present invention is useful.

[0095] In this invention (including the embodiments described later), the "surface roughness Ra" was measured using a non-contact surface shape measuring instrument (NewView7200, Zygo) with a lens magnification of 50x, an evaluation length of 100 μm, and a Gaussian filter of 25 μm. All other measurements were performed in accordance with JIS B0601 (Geometrical Characteristics Specifications of Products - Surface Properties).

[0096] 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. [Examples]

[0097] The present invention will be specifically described by examples and comparative examples, but the present invention is not limited thereto.

[0098] Preparation of inorganic pigment-encapsulated particles <Titanium dioxide-containing urethane resin particles (urethane Ti)> Titanium dioxide-containing urethane resin particles were prepared according to a method conforming to Patent Document 2. The titanium dioxide content was 35% by mass relative to the mass of the resin particles.

[0099] <Titanium dioxide-containing acrylic resin particles (Acrylic Ti)> Titanium dioxide-containing acrylic resin particles were prepared by a method conforming to Patent Document 2. The titanium dioxide content was 35% by mass relative to the mass of the resin particles.

[0100] <Titanium dioxide-containing glass particles (glass Ti)> A stock solution was prepared by dispersing titanium dioxide in a silica and water solution. This stock solution was then dropped into a heated oil bath and cured, followed by firing at 200°C, pulverization, and classification to produce titanium dioxide-containing glass particles. The titanium dioxide content was 35% by mass relative to the mass of these particles.

[0101] Table 1 shows the details of the inorganic pigment-encapsulated particles that were prepared.

[0102] [Table 1]

[0103] Preparation of water-based ink compositions for ballpoint pens <Example 1> An aqueous ballpoint pen ink composition of Example 1 was prepared using 15 parts by mass of titanium dioxide-encapsulated urethane resin particles (urethane Ti), 10 parts by mass of titanium dioxide as an inorganic pigment (average particle size 0.2 μm), 5 parts by mass of acrylic hollow particles (average particle size 0.2 μm), 10 parts by mass of styrene acrylic resin as a dispersant, 5 parts by mass of glycerin as an organic solvent, 1 part by mass of aminomethylpropanol as a pH adjuster, 1 part by mass of phosphate ester as a surfactant, 0.1 parts by mass of a silicone-based surfactant as an antifoaming agent, 0.1 parts by mass of sodium benzoate as a preservative, 0.2 parts by mass of xanthan gum as a viscosity modifier, and 52.6 parts by mass of distilled water.

[0104] <Examples 2-5 and Comparative Examples 1-2> Aqueous ink compositions for ballpoint pens for Examples 2-5 and Comparative Examples 1-2 were prepared in the same manner as in Example 1, except that the content of each component was changed as shown in Table 2.

[0105] The viscosity of the prepared water-based ink composition for ballpoint pens was measured using an ELD viscometer at a temperature of 25°C and a shear rate of 3.8 s. -1 The measurements were taken under the following conditions.

[0106] "evaluation" The prepared water-based ink composition for ballpoint pens was filled into ballpoint pens with a ball diameter of 0.38 mm, and the following evaluations were performed.

[0107] <Suppression of tip wear> The fabricated ballpoint pens were used for mechanical writing until the end of writing, and the wear of the ball bearing was measured using a measuring microscope. The evaluation criteria are as follows: A: The wear of the ball bearing seat was less than 5 μm. B: The wear of the ball bearing seat was between 5 μm and 15 μm. C: The wear of the ball bearing seat was 15 μm or more.

[0108] <Resistance to colorant settling> Initial lines were obtained by handwriting using the prepared ballpoint pen. Next, the ballpoint pen was left standing at 25°C for 6 months with the nib facing downwards. Handwriting was then performed using the ballpoint pen after this period, and a visual comparison was made with the initial lines. The evaluation criteria were as follows: A: The density of the lines did not change from the initial state. B: The ink density was slightly lighter than initially, but it was still usable for writing. C: The density of the lines was significantly lighter than initially, or there were writing problems.

[0109] <Color development> The color development was evaluated sensorily by visually inspecting the lines drawn using the ballpoint pens that were created. The evaluation criteria are as follows: A: The lines were sufficiently dark. B: The lines were too dark. C: The line density was too light.

[0110] The configurations and evaluation results of the examples and comparative examples are shown in Tables 2 and 3.

[0111] [Table 2]

[0112] [Table 3]

[0113] Table 1 shows that the water-based ink compositions for ballpoint pens in Examples 1 to 5 can suppress wear of the ballpoint pen tip while using hard inorganic pigments.

[0114] In particular, Examples 1-3 and 5, which contain hollow particles, exhibit especially good color development.

Claims

1. It contains at least resin particles and an inorganic pigment composed of an inorganic compound having a Mohs hardness of 5.5 or higher. The ratio of the average particle diameter of the resin particles to the average particle diameter of the inorganic pigment is 2.0 or more, and The average particle size of the resin particles and the inorganic pigment is the volume-average particle size Mv obtained from the scattering intensity distribution measured by laser diffraction. A water-based ink composition for ballpoint pens.

2. The aqueous ink composition for ballpoint pens according to claim 1, wherein at least a portion of the resin particles contain an inorganic pigment.

3. The aqueous ink composition for ballpoint pens according to claim 1 or 2, wherein the resin constituting the resin particles is at least one selected from the group consisting of urethane resin, urea resin, urea / urethane resin, melamine resin, acrylic resin, and olefin resin.

4. The aqueous ink composition for ballpoint pens according to claim 1 or 2, further containing hollow resin particles.

5. The aqueous ink composition for ballpoint pens according to claim 1 or 2, wherein the ratio of the circularity of the resin particles to the circularity of the inorganic pigment is 1.2 or more.

6. Temperature 25℃, shear rate 3.8s －１ The aqueous ink composition for ballpoint pens according to claim 1 or 2, wherein the viscosity measured under the specified conditions is 300 to 3000 mPa·s.

7. A ballpoint pen having the aqueous ink composition for ballpoint pens described in claim 1 or 2.

8. The ballpoint pen according to claim 7, wherein the ball diameter is 0.7 mm or less.

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