JP2024047660A - Water-based pigment ink composition - Google Patents

Abstract

[Problem] To provide an aqueous pigment ink composition which inhibits the occurrence of cissing and shrinkage of handwriting when written on a non-absorbent surface, has good adhesion and drying properties of handwriting to non-absorbent surfaces, and exhibits little change in color tone before and after drying of the handwriting. [Solution] An aqueous pigment ink composition for a writing instrument, comprising an organic pigment, a wetting agent, and a resin, wherein the resin comprises one or more types selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins, the organic pigment content is 3.0% by mass or more and 15.0% by mass or less, the wetting agent content is more than 0% by mass and 8.0% by mass or less, the content VR (volume %) of the one or more types of resin selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins and the organic pigment content VP (volume %) satisfies the following formula: VR/VP≧1.00, and the viscosity is 2.0 mPa·s or more and 10.0 mPa·s or less. [Selected Figure] None

Description

The present invention relates to an aqueous pigment ink composition for writing instruments.

Since aqueous pigment ink compositions for writing instruments have been used mainly on absorbent surfaces such as paper, the principle of drying handwriting by penetration into the absorbent surface has been mainly adopted. For this reason, aqueous pigment ink compositions for writing instruments currently contain no resin or only a small amount of resin, and contain a large amount of a wetting agent to impart penetrability to the absorbent surface.
Also, some markers are known that use aqueous pigment ink compositions for writing instruments that can be used to write on non-absorbent surfaces. However, these markers have problems such as a change in color tone between immediately after writing and after drying, problems with adhesion of handwriting to non-absorbent surfaces, repelling depending on the board surface being written on, and shrinkage of handwriting.
For this reason, oil-based ink compositions containing organic solvents are still primarily used as ink compositions for writing instruments that write on non-absorbent surfaces, and it has been considered difficult to replace them with water-based ink compositions.

Patent Document 1 describes an aqueous pigment ink composition for writing instruments that contains a pigment, water, a dispersion resin, a silicone-based resin emulsion, and another resin emulsion, in which the silicone-based resin emulsion and the other resin emulsion are used in combination in amounts such that the mass ratio of the solids is silicone-based resin emulsion/other resin emulsion = 0.1 to 0.8, and the viscosity, measured with a cone-plate type rotational viscometer at 25°C and 50 rpm, is greater than 2.0 mPa·s and less than 8.0 mPa·s. This aqueous pigment ink composition is said to provide lines drawn on a non-absorbent surface such as a PET film with superior abrasion resistance compared to lines drawn with conventional aqueous pigment ink compositions.

JP 2019-014769 A

The aqueous pigment ink composition described in Patent Document 1 was not satisfactory in terms of shrinkage of handwriting when written on a non-absorbent surface, and change in color tone before and after drying of handwriting. In addition, since a resin emulsion is used, if the pen is left with the cap removed, a resin film may form on the pen tip, causing smearing. The smearing caused by this is difficult to eliminate.
The problem that the present invention aims to solve is to provide an aqueous pigment ink composition which suppresses the occurrence of repelling and shrinkage of handwriting when written on a non-absorbent surface, has good adhesion to and drying properties of handwriting on non-absorbent surfaces, and exhibits little change in color tone before and after drying of the handwriting.

As a result of intensive research aimed at solving the above problems, the present inventors have found that the above problems can be solved by a specific aqueous pigment ink composition for a writing instrument, and have thus completed the present invention.
[Item 1]
Contains organic pigments, wetting agents and resins,
The resin contains at least one resin selected from the group consisting of an ammonia-neutralized (meth)acrylic resin and an ammonia-neutralized maleic acid resin,
The content of the organic pigment is 3.0% by mass or more and 15.0% by mass or less,
The content of the wetting agent is more than 0% by mass and 8.0% by mass or less,
The content V _R (volume %) of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins and the content V _P (volume %) of the organic pigment are expressed by the following formula:
V _R /V _P ≧1.00
The filling,
The viscosity is 2.0 mPa·s or more and 10.0 mPa·s or less.
A water-based pigment ink composition for a writing instrument.
[Item 2]
Item 2. The aqueous pigment ink composition for a writing instrument according to item 1, having a surface tension of 35.0 N/m or less.
[Item 3]
Item 3. An aqueous pen having a core containing the aqueous pigment ink composition for a writing instrument according to item 1 or 2.

The present invention provides an aqueous pigment ink composition which suppresses the occurrence of repelling and shrinkage of handwriting when written on a non-absorbent surface, exhibits good adhesion to and drying properties of handwriting on non-absorbent surfaces, and exhibits little change in color tone before and after drying of the handwriting.
In addition, because a resin solution is used, even if the pen is left with the cap removed and a resin film forms on the pen tip, causing smudging, it is possible to remove the smudging over time by putting the cap back on.

The present inventors began to investigate the issue, believing that the change in color tone of the handwriting before and after drying is a problem between the organic pigment and the resin, that the adhesion of the handwriting to non-absorbent surfaces is a problem with the resin, and that the occurrence of cissing of the handwriting on non-absorbent surfaces is a problem with the physical properties of the entire aqueous pigment ink composition for writing instruments.
The present inventors have discovered that in an aqueous pigment ink composition for a writing instrument containing a specific resin, the change in color tone before and after drying of handwriting is determined by the volume of the organic pigment in the aqueous pigment ink composition for a writing instrument and the volume of the resin in the aqueous pigment ink composition for a writing instrument, and that the content V R (volume %) of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins and the content V _P (volume %) of the organic pigment in the aqueous pigment ink composition for a writing _instrument can be calculated by the formula (1);
V _R / V _P ≧ 1.00 (1)
It was found that by satisfying the above condition, the change in color tone before and after the writing is dried can be reduced.
The present inventors also discovered that in the case of an aqueous pigment ink composition for a writing instrument with a high organic pigment concentration, the resin content is high when formula (1) is followed, and therefore the viscosity of the aqueous pigment ink composition for a writing instrument becomes too high in a core-type writing instrument, which may result in smudging; they also discovered that by using a specific resin and adjusting the content of the humectant, it is possible to construct an aqueous pigment ink composition for a writing instrument which has a high concentration of organic pigment but a low viscosity.
Furthermore, the present inventors have found that by specifying the content of the humectant, it is possible to suppress the occurrence of cissing of handwriting on non-absorbent surfaces, suppress shrinkage of handwriting, and improve the drying properties of handwriting; by using a component containing one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins as the resin, and in particular by containing a specific amount of one or more resins (wherein the counter ion is ammonium) selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins, it is possible to improve the drying properties of handwriting on non-absorbent surfaces; and by setting the surface tension to a specific value or less, it is possible to suppress the occurrence of cissing of handwriting on non-absorbent surfaces.
These findings provide a solution to all of the problems that arise when an aqueous pigment ink composition for writing instruments is used to write on a non-absorbent surface, making this an extremely useful invention.

[Water-based pigment ink composition for writing instruments]
The aqueous pigment ink composition for a writing instrument of the present invention comprises:
Contains organic pigments, wetting agents and resins,
The resin contains at least one resin selected from the group consisting of an ammonia-neutralized (meth)acrylic resin and an ammonia-neutralized maleic acid resin,
The content of the organic pigment is 3.0% by mass or more and 15.0% by mass or less,
The content of the wetting agent is more than 0% by mass and 8.0% by mass or less,
The content V _R (volume %) of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins, and the content V _P (volume %) of the organic pigment are expressed by the formula (1);
V _R / V _P ≧ 1.00 (1)
The filling,
The viscosity is 2.0 mPa·s or more and 10.0 mPa·s or less.
The aqueous pigment ink composition for a writing instrument of the present invention may have a surface tension of 35.0 N/m or less.
The details will be explained below.

<Organic pigments>
As the organic pigment, one or more of various organic pigments that have been used in aqueous pigment ink compositions for writing instruments in the past can be used to obtain a desired color tone. In addition, in the present invention, colored resin particles can be used as the organic pigment.
Examples of the organic pigment in the present invention include at least one selected from the group consisting of color pigments such as carbon black, phthalocyanine-based, azo-based, anthraquinone-based, quinacridone-based, isoindolinone-based, diketopyrrolopyrrole-based, dioxane-based, indigo-based, thioindigo-based, perinone-based, perylene-based, indolenone-based, and azomethine-based pigments, and fluorescent pigments.
The colored resin particles are spherical, amorphous, hollow, flat, or other shaped resin particles colored with one or more inorganic pigments, organic pigments, or dyes that exhibit any color tone, as required. When the resin particles themselves have a desired color tone, they can be used without coloring. Examples of resin materials that form the colored resin particles include one or more selected from the group consisting of polyethylene-based resins, polypropylene-based resins, polystyrene-based resins, vinyl chloride-based resins, poly(meth)acrylate-based resins, benzoguanamine-based resins, melamine-based resins, polyurethane-based resins, and polyamide-based resins (nylon, etc.). The colored resin particles are present in a predetermined shape without dissolving in the aqueous pigment ink composition for writing instruments. Examples of inorganic pigments, organic pigments, or dyes used to color the resin particles to any color tone, as required, include one or more selected from the group consisting of the organic pigments, inorganic pigments described below, and dyes described below.

The content of the organic pigment is 3.0% by mass or more and 15.0% by mass or less, based on 100% by mass of the total amount of the aqueous pigment ink composition for writing instruments. It is preferably 4.0% by mass or more, more preferably 5.0% by mass or more, and preferably 13.0% by mass or less, more preferably 12.0% by mass or less. If the content of the organic pigment is less than 3.0% by mass, the color tone of the aqueous pigment ink composition for writing instruments may be too light and the desired color tone may not be achieved, resulting in poor color development. If the pigment content exceeds 15.0% by mass, the adhesion of the writing marks of the aqueous pigment ink composition for writing instruments to non-absorbent surfaces may be poor.

<Resin>
The aqueous pigment ink composition for a writing instrument of the present invention contains a resin for dispersing the pigment, increasing the viscosity, fixing the handwriting on a suitable writing surface when the solvent evaporates after writing on the writing surface, etc. The resin contains one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins.

The mass average molecular weight of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins is not particularly limited. For example, it is 1,000 or more, preferably 1,500 or more, and for example, 25,000 or less, preferably 20,000 or less. If the mass average molecular weight of the resin exceeds 25,000, the adhesiveness of the handwriting may decrease.

The acid value of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins is not particularly limited. For example, it is 120 or more, preferably 150 or more, and for example, 700 or less, preferably 550 or less. If the acid value of the resin is less than 120, the viscosity of the aqueous pigment ink composition for writing instruments may increase, and the adhesion of the handwriting may decrease.

The ammonia-neutralized (meth)acrylic resin is a resin obtained by polymerizing a monomer component containing at least (meth)acrylic acid. Examples of the monomer other than (meth)acrylic acid include one or more selected from the group consisting of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene, acrylic acid alkyl ester monomers such as methyl (meth)acrylate, acrylic acid ester monomers having functional groups such as hydroxyethyl (meth)acrylate and dimethylaminoethyl (meth)acrylate, and olefin monomers such as ethylene.
The ammonia-neutralized (meth)acrylic resin is preferably, for example, a resin obtained by neutralizing one or more resins selected from the group consisting of styrene-(meth)acrylic acid resins, (meth)acrylic acid ester-(meth)acrylic acid resins, and styrene-(meth)acrylic acid ester-(meth)acrylic acid resins with ammonia. The neutralization rate of ammonia is 100 mol% or less, preferably 80 mol% or less, and for example 50 mol% or more, preferably 60 mol% or more, based on 100 mol% of the total amount of carboxyl groups in the resin.

The ammonia-neutralized (meth)acrylic resin may be a commercially available (meth)acrylic resin neutralized with ammonia, or a commercially available product that has been neutralized with ammonia in advance. Examples include commercially available products such as Seiko PMC's Hi-Loss series and BASF's Joncryl series that have been neutralized with ammonia.

The ammonia-neutralized maleic acid resin is a resin obtained by polymerizing a monomer component containing at least maleic acid (anhydride). Examples of the monomer other than maleic acid (anhydride) include one or more selected from the group consisting of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene, acrylic acid alkyl ester monomers such as methyl (meth)acrylate, acrylic acid ester monomers having functional groups such as hydroxyethyl (meth)acrylate and dimethylaminoethyl (meth)acrylate, and olefin monomers such as (meth)acrylic acid and ethylene.
The ammonia-neutralized maleic acid resin is preferably, for example, a resin obtained by neutralizing one or more resins selected from the group consisting of styrene-(anhydrous)maleic acid resins, (meth)acrylic acid ester-(anhydrous)maleic acid resins, and styrene-(meth)acrylic acid ester-(anhydrous)maleic acid resins with ammonia. The neutralization rate of ammonia is 100 mol% or less, preferably 80 mol% or less, for example 50 mol% or more, preferably 60 mol% or more, based on 100 mol% of the total amount of carboxyl groups in the resin.

The ammonia-neutralized maleic acid resin may be a commercially available (anhydrous) maleic acid resin neutralized with ammonia, or a commercially available product that has already been neutralized with ammonia. Examples include the X series manufactured by Seiko PMC Corporation that has been neutralized with ammonia, and the SMA series manufactured by Atofina (e.g., SMA1000H).

The content of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins in the aqueous pigment ink composition for writing instruments is represented by the above formula (1);
V _R / V _P ≧ 1.00 (1)
(wherein V _R is the content (volume %) of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins, and V _P is the content (volume %) of the organic pigment. With the total amount of the aqueous pigment ink composition for writing instruments taken as 100 mass%, the content of one or more resins (solid content) selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins is, for example, 1.0 mass% or more, preferably 3.0 mass% or more, and more preferably 4.0 mass% or more, and for example, 20.0 mass% or less, preferably 15.0 mass% or less, and more preferably 13.0 mass% or less. If the content of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins is less than 1.0 mass %, the adhesion of the handwriting of the aqueous pigment ink composition for a writing instrument to a non-absorbent surface may deteriorate, the change in color tone of the handwriting before and after drying may be significant, the viscosity of the aqueous pigment ink composition for a writing instrument may be reduced, the amount of ink flowing out during writing may be inappropriate, causing bleeding, ink leakage, or the handwriting may not be formed.

<Wetting Agent>
The aqueous pigment ink composition for a writing instrument of the present invention contains a wetting agent for adjusting the viscosity and the drying properties of the writing marks.
The wetting agent is not limited as long as it is used in aqueous pigment ink compositions for writing instruments, particularly in aqueous marking pens and aqueous felt-tip pens. For example, one or more selected from the group consisting of polyhydric alcohols such as glycerin, diglycerin, triglycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, and polypropylene glycol, sugars such as sorbitol, ureas such as urea, and derivatives thereof can be used.
In the present invention, it is preferable to use one or more selected from the group consisting of ethylene glycol, glycerin, propylene glycol, and diethylene glycol, and particularly preferably one or more selected from the group consisting of ethylene glycol, glycerin, and propylene glycol.

The content of the humectant in the aqueous pigment ink composition for writing instruments is more than 0% by mass and not more than 8.0% by mass, with the total amount of the aqueous pigment ink composition for writing instruments being 100% by mass. For example, it is 0.5% by mass or more, preferably 1.0% by mass or more, more preferably 2.0% by mass or more, for example, 7.8% by mass or less. If the content of the humectant exceeds 8.0% by mass, the dispersion of each component in the aqueous pigment ink composition for writing instruments becomes unstable, the drying speed of the handwriting decreases, and the drying property of the handwriting may decrease, the viscosity of the aqueous pigment ink composition for writing instruments may increase, and the amount of ink flowing out during writing may become inappropriate, causing smearing, etc.

<Water>
The aqueous pigment ink composition for writing instruments contains water that functions as a solvent to dissolve or disperse the components. Examples of water that can be used include tap water, purified water, distilled water, ion-exchanged water, and pure water. Preferably, pure water, ion-exchanged water, distilled water, etc. are used.

The water content can be adjusted appropriately depending on the content and viscosity of each component in the aqueous pigment ink composition for writing instruments. For example, the water content is 40.0% by mass or more, preferably 50.0% by mass or more, and 90.0% by mass or less, preferably 85.0% by mass or less, with the total amount of the aqueous pigment ink composition for writing instruments being 100% by mass. If the water content is less than 40.0% by mass, the viscosity of the aqueous pigment ink composition for writing instruments may increase, the amount of ink flowing out during writing may become inappropriate, causing smearing, and storage stability may decrease. If the water content exceeds 90.0% by mass, the viscosity of the aqueous pigment ink composition for writing instruments may decrease, the amount of ink flowing out during writing may become inappropriate, causing bleeding, and ink leakage may occur.

<Surfactant>
The aqueous pigment ink composition for a writing instrument of the present invention may contain a surfactant in order to improve storage stability, adjust viscosity, and improve dispersibility of the pigment.
The surfactant may be any of anionic, nonionic, and amphoteric surfactants. For example, one or more selected from the group consisting of anionic surfactants such as sulfonic acid surfactants (e.g., alkylarylsulfonic acid (salt), sulfosuccinic acid ester, sulfosuccinic acid diester, etc.), phosphorus surfactants (e.g., alkyl phosphate ester, alkyl ether phosphate ester, alkylaryl phosphate ester, etc.), nonionic surfactants such as ether surfactants (polyoxyalkylene alkyl ether, etc.), acetylene glycol surfactants, and ester surfactants (polyoxyalkylene fatty acid ester, polyoxyalkylene alkylaryl ether, sorbitan fatty acid ester, glycerin fatty acid ester, etc.), and fluorine-based surfactants may be used.
In the present invention, among these surfactants, one or more selected from the group consisting of anionic surfactants (e.g., sulfonic acid surfactants) and nonionic surfactants (e.g., acetylene glycol surfactants) are preferably used in terms of wetting/penetrating function, emulsifying function, dispersing function, etc.

The content of the surfactant is not particularly limited. It is 1.5% by mass or less, preferably 1.0% by mass or less, and more preferably 0.7% by mass or less, with the total amount of the aqueous pigment ink composition for writing instruments being 100% by mass. If the content of the surfactant exceeds 1.5% by mass, bleeding or show-through may occur when writing on the paper, the amount of ink flowing out during writing may be inappropriate, causing bleeding, or ink leakage may occur.

<Other additives>
The aqueous pigment ink composition for writing instruments of the present invention may contain other additives as necessary, as long as they do not affect various properties when written on a non-absorbing surface or the change in color tone before and after drying of the writing. The other additives are not particularly limited as long as they are used in aqueous pigment ink compositions for writing instruments. For example, one or more selected from the group consisting of preservatives, antifungal agents, pH adjusters, colorants other than organic pigments, water-soluble organic solvents other than wetting agents, resins other than the above-mentioned resins, rust inhibitors, viscosity adjusters (thickening agents/thickening inhibitors), chelating agents, lubricants, defoamers, leveling agents, ultraviolet absorbers, infrared absorbers, antioxidants, and fluorescent whitening agents may be contained in an appropriate amount.

The preservatives and antifungal agents are blended to improve the storage stability of the aqueous pigment ink composition for writing instruments and to prevent corrosion and mold growth in the aqueous pigment ink composition for writing instruments. Examples of the preservatives and antifungal agents include one or more selected from the group consisting of benzoisothiazoline-based preservatives and antifungal agents, pentachlorophenol-based preservatives and antifungal agents, cresol-based preservatives and antifungal agents, propylene glycol-based preservatives and antifungal agents, iodine-based preservatives and antifungal agents, etc.

The pH adjuster is blended to adjust the pH value of the aqueous pigment ink composition for writing instruments and to prevent the aqueous pigment ink composition for writing instruments from gelling. Examples of the pH adjuster include at least one selected from the group consisting of sodium hydroxide, sodium carbonate, sodium phosphate, sodium acetate, triethanolamine, aminomethylpropanol, etc.

The colorant other than the organic pigment may be, for example, one or more selected from the group consisting of inorganic pigments and dyes.
Examples of inorganic pigments include one or more selected from the group consisting of graphite, titanium oxide, zinc oxide, red iron oxide, yellow iron oxide, ultramarine, Prussian blue, metal powders such as aluminum powder and bronze powder, extender pigments such as talc, silica, alumina, mica, and alumina silicate, fluorescent pigments, glass flakes, and luster pigments.
The dye may be at least one selected from the group consisting of direct dyes, acid dyes, food dyes, basic dyes, and the like.

<Water-soluble organic solvent>
The aqueous pigment ink composition for a writing instrument of the present invention may contain a water-soluble organic solvent in order to improve storage stability, adjust viscosity, and improve dispersibility of the pigment.
The water-soluble organic solvent is an organic solvent having a solubility in water at 20° C. of 1 g/L or more, preferably 10 g/L or more, more preferably 100 g/L or more, and most preferably a solvent that is uniformly miscible in any ratio, other than the compounds listed as the wetting agents above. Examples of the water-soluble organic solvent include one or more selected from the group consisting of monoalcohols, lower alkyl ethers of polyhydric alcohols having 1 to 6 carbon atoms, ketones, ethers, esters, nitrogen-containing compounds, and the like.

<Ratio V R /V P of the content V _R (vol %) of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins to the content V _P (vol %) of organic _pigment in an aqueous pigment ink composition for writing _instruments >
The ratio V R /V P of the content V _R (volume %) of one or more resins selected from the group consisting of _ammonia -neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins to the content V _P (volume % ₎ of the organic pigment in the aqueous pigment ink composition for writing instruments is expressed by the following formula (1);
V _R / V _P ≧ 1.00 (1)
The ratio V _R /V _P is preferably 1.00 or more, more preferably 1.20 or more, and even more preferably 1.40 or more, and is preferably 4.00 or less, more preferably 3.00 or less, and even more preferably 2.50 or less. By setting the ratio V _R /V _P in this range, it is possible to reduce the change in color tone before and after drying of the handwriting.

<Viscosity of Water-Based Pigment Ink Composition for Writing Instruments>
The viscosity of the aqueous pigment ink composition for a writing instrument of the present invention is from 2.0 mPa·s to 10.0 mPa·s, particularly from 2.2 mPa·s or more, preferably from 2.6 mPa·s or more, and from 9.5 mPa·s or less, preferably from 9.3 mPa·s or less.
If the viscosity of the aqueous pigment ink composition for writing instruments is less than 2.0 mPa·s, the ink may flow out of the tip of the writing instrument excessively, making it difficult to form accurate handwriting (short writing distance, thick line width, etc.), the drying speed may be slow, repelling may occur when writing on a non-absorbent surface, and shrinkage of the handwriting may be large when writing on a non-absorbent surface. If the viscosity of the aqueous pigment ink composition for writing instruments is more than 10.0 mPa·s, the viscosity may be too high, causing blurring of the handwriting, the ink may not flow out of the tip of the writing instrument, and problems may arise in terms of ink handleability, sedimentation stability, production costs, etc.
The viscosity of the aqueous pigment ink composition for writing instruments can be adjusted to a desired value, for example, by adjusting the contents of the resin, pigment, wetting agent, and water.
The viscosity of the aqueous pigment ink composition for writing instruments can be measured, for example, based on the viscosity measuring method described in the Examples below.

<Surface tension of aqueous pigment ink composition for writing implement>
The surface tension of the aqueous pigment ink composition for writing instruments of the present invention is not particularly limited. For example, it is 40.0 N/m or less, preferably 38.0 N/m or less, more preferably 35.0 N/m or less. By making the surface tension 40.0 N/m or less, it is possible to suppress the occurrence of repelling when writing on a non-absorbent surface.
The surface tension of the aqueous pigment ink composition for writing instruments can be adjusted to a desired value, for example, by adjusting the type and content of the wetting agent and the type and content of the surfactant, etc., which are contained as necessary.
The surface tension of the aqueous pigment ink composition for writing instruments can be measured, for example, based on the viscosity measuring method described in the Examples below.

<Method for producing aqueous pigment ink composition for writing instruments>
The method for producing the aqueous pigment ink composition for a writing instrument of the present invention is not particularly limited.
For example, all of the components constituting the aqueous pigment ink composition for a writing instrument can be placed in a container and mixed, stirred and dispersed using a mixing/stirring device such as a ball mill, a bead mill, a roll mill, a Henschel mixer, a homomixer, a propeller stirrer, a homogenizer, a high-pressure homogenizer, a kneader or a dissolver to prepare the aqueous pigment ink composition for a writing instrument.

For example, some of the components of the aqueous pigment ink composition for writing instruments, such as pigment, resin, and water, can be placed in a container and mixed, stirred, and dispersed using the mixing and stirring device to produce a color base (pigment paste, pigment dispersion), and then the remaining components can be added and mixed and stirred to prepare the aqueous pigment ink composition for writing instruments.
In the present invention, a method is preferably used in which a color base containing at least the pigment, a part of the resin, a wetting agent and water is produced, and then the color base, the remainder of the resin and the other components are mixed and stirred to produce the color base. This makes it possible to easily adjust the degree of dispersion of the pigment (dispersed particle size) at the color base production stage.
In preparing the aqueous pigment ink composition for writing instruments, coarse particles, gas, and air bubbles may be removed by filtration, centrifugation, degassing, etc. In preparing the aqueous pigment ink composition for writing instruments, means such as heating, cooling, pressurization, decompression, and inert gas replacement may also be used. Furthermore, an aging process may be performed after preparing the aqueous pigment ink composition for writing instruments.

[Water-based pen]
An aqueous pen comprising the aqueous pigment ink composition for a writing instrument of the present invention is an aqueous pen comprising a pen tip consisting of a fiber core or a plastic core, and an ink reservoir, in which the aqueous pigment ink composition for a writing instrument is contained.
The aqueous pigment ink composition for a writing instrument of the present invention can be suitably used, in particular, as an aqueous pigment ink composition for a core-type writing instrument.
The aqueous pigment ink composition for a writing instrument of the present invention can be suitably used, for example, as an aqueous marking pen or an aqueous felt tip pen.
Examples of water-based marking pens and water-based felt-tip pens include writing implements also known as felt pens, which have a pen tip made of a fiber bundle, a sintered body, or a plastic, and which are provided with an ink storage means in the main body made of a felt or fiber bundle that is impregnated with ink, and which supply ink from such an ink storage means to the pen tip by utilizing capillary action to enable writing, i.e., so-called core-type pens. Also included are non-core-type or so-called free-ink-type pens in which ink is stored directly in the cylindrical main body and supplied to the pen tip.
The aqueous pigment ink composition for writing instruments according to the present invention can be suitably used in both of these water-based marking pens and water-based felt-tip pens.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

The components constituting the aqueous pigment ink compositions for writing instruments according to the Examples and Comparative Examples are as follows.
Organic pigment 1: Pigment Black 7
Organic pigment 2: Pigment Blue 15
Organic pigment 3: Pigment Red 254
Organic pigment 4: Pigment Violet 23
Organic pigment 5: Pigment Red 267
Resin 1: Resin liquid (concentration 34% by mass) containing an ammonia neutralized styrene-(meth)acrylic acid-based resin (mass average molecular weight 16,500, acid value 240)
Resin 2: Resin liquid (concentration 34% by mass) containing an ammonia neutralized styrene-(meth)acrylic acid-based resin (mass average molecular weight 8,500, acid value 200)
Resin 3: Resin liquid (concentration 34% by mass) containing an ammonia neutralized styrene-(meth)acrylic acid-based resin (mass average molecular weight 1,700, acid value 238)
Resin 4: Resin liquid (concentration 34% by mass) containing an ammonia neutralized styrene-maleic anhydride resin (mass average molecular weight 5,500, acid value 480)
Resin 5: Resin liquid (concentration 20% by mass) containing a styrene-(meth)acrylic acid-based resin (mass average molecular weight 8,000, acid value 160) neutralized with sodium hydroxide
Resin 6: Resin liquid (concentration 34% by mass) containing a styrene-(meth)acrylic acid-based resin (mass average molecular weight 8,500, acid value 200) neutralized with sodium hydroxide
Wetting agent 1: Ethylene glycol Wetting agent 2: Glycerin Wetting agent 3: Urea Wetting agent 4: Phosphate ester compound Surfactant 1: Sodium dialkyl sulfosuccinate Surfactant 2: Acetylene glycol compound pH adjuster: Triethanolamine Preservative: Proxel XL-2, manufactured by Lonza Japan
・Mold inhibitor: Courtside PH2, manufactured by Osaka Gas Chemicals

[Examples 1 to 6, Comparative Examples 1 to 5]
Preparation of the Pigment Base
The organic pigment shown in Table 1 in the amount shown in Table 1, the resin liquid shown in Table 1 in an amount equal to half the amount shown in Table 1, and the wetting agent shown in Table 1 in the amount shown in Table 1 were each placed in a container and dispersed and mixed in a bead mill to prepare an organic pigment base.

<Preparation of Water-Based Pigment Ink Composition for Writing Instruments>
Example 1
The components other than the organic pigment, resin liquid, and wetting agent were each placed in the amounts shown in Table 1, the total amount of the organic pigment base obtained in the preparation of the pigment base, and half the amount of the resin liquid shown in Table 1 were each placed in a container and mixed with a stirrer. Coarse particles in the ink were removed using a high-speed centrifuge to prepare the aqueous pigment ink composition for writing instruments of Example 1.

(Examples 2 to 5, Comparative Examples 1 to 5)
The aqueous pigment ink compositions for writing instruments according to Examples 2 to 6 and Comparative Examples 1 to 5 were each prepared in the same manner as in Example 1, except that the components and blending amounts (parts) of the aqueous pigment ink compositions for writing instruments were as shown in Table 1.

<Preparation of water-based pen>
The tip was attached to the pen body (WBK-T container member, manufactured by Sakura Color Products Co., Ltd.), and a cap was also attached.
For each of the aqueous pigment ink compositions for writing instruments of Examples 1 to 6 and Comparative Examples 1 to 5, a center core was filled with each of the compositions, which was then inserted into a pen body and a tail plug was attached to prepare three aqueous pens for each aqueous pigment ink composition for writing instruments.

[evaluation]
The aqueous pigment ink compositions for writing instruments of Examples 1 to 6 and Comparative Examples 1 to 5 were evaluated as follows. The results are also shown in Table 1. Note that in Comparative Example 5, no handwriting could be obtained, and therefore it was not possible to evaluate the adhesion of the handwriting and the color tone before and after drying of the handwriting.

<Writability>
For each aqueous pigment ink composition for writing instruments, a line was drawn on a polyvinyl chloride resin sheet using the prepared aqueous pen, and the state of the handwriting was visually evaluated. The results are also shown in Table 1. In the present invention, A is pass and C is fail.
A: There is no repelling of the handwriting, and no shrinkage of the handwriting is observed.
C: Repelling of handwriting has occurred, and handwriting shrinkage has also been observed.

<Handwriting adhesion>
For each aqueous pigment ink composition for writing instruments, a line was drawn on a polyvinyl chloride resin sheet using the prepared aqueous pen, and the written mark was left to dry for one day, then rubbed strongly up and down with a finger, and the peeling state of the written mark was observed and evaluated. The results are also shown in Table 1. In the present invention, A is pass, and B and C are fail.
A: No peeling of handwriting is observed.
B: A small amount of handwriting peeling is observed.
C: Peeling of handwriting is observed overall.

<Color tone before and after writing dry>
For each aqueous pigment ink composition for writing instruments, a line was drawn on white art paper using the prepared aqueous pen, and the line was left to dry for 1 hour, and the line was visually compared with the line immediately after the line was drawn on the white art paper, and the color tone before and after the line was dried was evaluated according to the following criteria. The results are also shown in Table 1. In the present invention, A is pass, and B and C are fail.
A: Even when compared side by side, the difference in the color of the handwriting cannot be distinguished.
B: When compared side by side, the difference in the color of the handwriting can be distinguished.
C: The difference in color of the handwriting can be distinguished even when compared at a distance.

From Table 1, it can be seen that the aqueous pigment ink composition for writing instruments according to the present invention suppresses the occurrence of repelling and shrinkage of handwriting when written on a non-absorbent surface, has good adhesion and drying properties to the non-absorbent surface, and there is little change in color tone before and after the handwriting dries.

Claims (3)

Contains organic pigments, wetting agents and resins,
The resin contains at least one resin selected from the group consisting of an ammonia-neutralized (meth)acrylic resin and an ammonia-neutralized maleic acid resin,
The content of the organic pigment is 3.0% by mass or more and 15.0% by mass or less,
The content of the wetting agent is more than 0% by mass and 8.0% by mass or less,
The content V _R (volume %) of one or more resins selected from the group consisting of ammonia-neutralized (meth)acrylic resins and ammonia-neutralized maleic acid resins and the content V _P (volume %) of the organic pigment are expressed by the following formula:
V _R /V _P ≧1.00
The filling,
The viscosity is 2.0 mPa·s or more and 10.0 mPa·s or less.
A water-based pigment ink composition for a writing instrument. The aqueous pigment ink composition for writing instruments according to claim 1, which has a surface tension of 35.0 N/m or less. An aqueous pen having a core containing the aqueous pigment ink composition for a writing instrument according to claim 1 or 2.