JPH11140370A - Aqueous pigment ink for white board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aq. pigment ink for white boards in which an org. pigment is kept dispersed well for a long term and which enables smooth writing and enables written lines on white boards made of various materials to be wiped off and erased completely by dispersing an org. pigment, a specific polyvinyl alcohol as a dispersant, and three specific compds. as a release agent in an aq. medium. SOLUTION: This ink is prepd. by dispersing an org. pigment, a dispersant, and a release agent as essential ingredients in an aq. medium. Polyvinyl alcohol having a viscosity (of a 4% aq. soln.) of 3-60 cP and a degree of saponification of 75-90 mol.% is used as the dispersant. The release agent used comprises (a) a polyoxyethylene glycol monoalkyl ether having a 6-22C alkyl group and an HLB of 6-10, (b) an alkylamine acetate having a 8-20C alkyl group, and (c) D-mannitol. The ink comprises 72-92 wt.% aq. medium, 1.0-6.0 wt.% org. pigment, 0.15-6.0 wt.% dispersant, and 6.0-16 wt.% release agent, the sum being 100 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Ink used in a felt pen for drawing characters and figures on a white board is an application field of the present invention.

[0002]

[Prior Art] Draw letters and patterns on a blackboard with chalk,
Markers that can be erased by wiping the blackboard and rewritten when they are no longer needed have been used in daily life. In recent years, whiteboards and felt pens have been used in place of blackboards and chalks. The white plate has a non-absorbable and smooth surface, and its surface material is melamine resin, polyester resin, polypropylene resin, ceramics or the like. Conventionally, ink for a white plate used by being loaded into a felt pen is basically obtained by dispersing a pigment in an organic solvent such as ketones or alcohols, and is used for stable dispersion and handwriting fixation. Resins soluble in organic solvents are used. In addition, a high-boiling liquid material is blended as a release agent so that unnecessary handwriting can be wiped and erased with a cloth, soft paper, felt or the like. In recent years, there has been a long-awaited demand for aqueous inks that do not use organic solvents due to environmental pollution and harm to human bodies due to organic solvents, and they have already been commercialized with felt-tip pens and ball-point pens. But,
When these aqueous pigment inks are used on a white plate, the pigment color remains on the white plate even if the handwriting is to be wiped off, which is unsuitable because a so-called stain remains. In addition, aqueous pigment inks that have recently been proposed as aqueous pigment inks for white boards have not yet been put into practical use as commercial products because stains often remain thinly on the surface of the white board and are unsuitable.

[0003]

The present invention provides a water-based pigment ink for a white plate, which satisfies long-term dispersion stability of organic pigments and good writability, and completely eliminates wiping of handwriting on a white plate made of various materials. It is intended to realize ink that can be used.

[0004]

Means for Solving the Problems The present invention is to create a new release agent composition that can completely wipe off and erase handwriting on various white boards, while ensuring long-term dispersion stability of organic pigments and good writability. In order to solve the problem.

For various surface materials, an organic pigment, a dispersant, and a release agent are experimentally produced in combination with a conventionally known substance in an ink, and even when the handwriting on a white plate is wiped and erased, the color of the pigment remains faint. In many cases, an aqueous pigment ink for a white plate that can be used for various white plates has not been realized.

If the type of the white plate surface material is different, the affinity with the ink component is different, and the seemingly smooth surface is microscopically uneven with various curvatures depending on the type of the white plate surface material and the manufacturing method. This also affects the degree of affinity and thus the ease of handwriting wiping. The type and particle size of the pigment also differ in the degree of stain generation in relation to the type and surface condition of the white board surface material. It is not recognized that the type of the aqueous medium causes a difference in the degree of stain generation even when a solvent other than water is contained. The type and amount of the dispersant cause a difference in the degree of stain generation in relation to the surface of the white plate and the pigment. Furthermore, the release agent causes a difference in the degree of stain generation in relation to the surface of the white plate, the pigment and the dispersant. Even if the ink penetrates deeply into the fine recesses on the surface of the white plate, it causes stain. The ink after writing dries into a film, but the pigment must remain in the film, and the release agent must be interposed between the film and the white plate to facilitate wiping. However, if attention is paid only to stain, stable dispersibility of the pigment, which can be called the lifeline of the ink, cannot be secured. Staining occurs in this way with many factors associated with it, so the solution is by no means simple. The present invention has attempted to solve this difficulty by selecting the composition of the ink, and has found that it can be solved with a novel composition, and has reached the present invention.

In selecting an ink composition for a white plate on the premise of an aqueous medium, the first condition is to disperse the pigment and ensure its stability. Although it has been proposed to use various resins in whiteboard inks for both stable dispersion and film formation during ink drying, compatibility with various whiteboard materials and generation of stains in combination with the release agent described below should be avoided. In view of this, the present invention uses polyvinyl alcohol.
Moreover, the viscosity of the 4% aqueous solution is in the range of 1 cps to 60 cps and the saponification degree is 70 mol% to 95
Use polyvinyl alcohol in the range of mol% or less. Particularly preferred is polyvinyl alcohol having a viscosity of 3 to 30 cps and a saponification degree of 75 to 90 mol%. Less than 100% of the remaining mole percent is unsaponified residues of polyvinyl acetate, an intermediate in the production of polyvinyl alcohol. When the viscosity of the 4% aqueous solution is higher than the above range, the dispersion stability is further enhanced, but the writing performance with a felt pen is deteriorated. When the viscosity is too low, the dispersion stability and generation of stain are unsuitable. If the degree of saponification is out of the above range, stable dispersion cannot be ensured, which is inappropriate. Producing inks in various mixing ratios using resins other than polyvinyl alcohol soluble in an aqueous medium, for example, polyvinylpyrrolidone, polyacrylic acid and copolymers thereof, or styrene-maleic acid copolymer salts, etc., were satisfactory. There are no results to be achieved.

In the present invention, the release agent is composed of three members.
One component is a polyoxyethylene glycol monoalkyl ether having an HLB value of 6 or more and 10 or less. The alkyl group of this monoalkyl ether has 6 to 22 carbon atoms.
The following single or mixed alkyl groups have different HLB values depending on the type of the alkyl group and the number of moles added to the oxyethylene group.
, The HLB value falls within the above range. When the carbon number of the alkyl group and the HLB value are as described above, this compound exhibits an effective antistain action in cooperation with the other two of the release agents. When the HLB value is outside the above range, the effect of preventing stain is poor or equal to none, and the dispersion stability of the pigment is poor.
More preferably, the HLB value is 8 to 9.
Further, this component of the present invention improves the wetting of the ink on the surface of the white plate, and prevents the writing line from becoming thin during drying. When the carbon number of the alkyl group of the monoalkyl ether is out of the above range or in the case of alkylphenyl, HLB is used.
Even if the value is selected to be various values, it is not appropriate because only an ink having an unsatisfactory dispersion stability or stain of the pigment is obtained.
Particularly preferred is a case where the carbon number is 8 or more and 18 or less.

In the present invention, the alkylamine acetate as the second component of the release agent has an alkyl group having 8 carbon atoms.
It is an acetate salt of a single or mixed alkylamine of not less than 20 or more. When the number of carbon atoms is in the above range, this compound exhibits an effective antistain action in cooperation with the other two of the release agents. When the carbon number is outside the above range, the effect of preventing stain is poor or equal to none, and the dispersion stability of the pigment is poor. Salts of acids other than acetic acid, such as hydrochloride, have no stain-preventing effect
Moreover, it lacks dispersion stability. More preferred is an alkylamine acetate having 10 to 18 carbon atoms in the alkyl group.

[0010] The third component of the release agent in the present invention is D-
Mannitol. This compound effectively exerts an anti-stain action in cooperation with the other two of the release agents. Since it has a plurality of hydroxyl groups in the molecule, trimethylolpropane, pentaerythritol, sorbitol and the like were tested in place of D-mannitol, but there was no stain prevention effect, and similarly, dextrin and soluble starch have a stain prevention effect immediately after writing. However, when it was attempted to wipe off a few hours after writing, stain remained and was unsuitable.

The mechanism of action of the release agent in the present invention is unknown, but D-mannitol, a component thereof, precipitates as crystals as the ink dries after writing, and the adhesion of the ink to the surface of the white plate and the penetration of fine recesses are moderate. It seems that it is possible to completely wipe off the handwriting by preventing in the range. The other two release agents have a slight anti-stain effect on their own, but the effect of promoting the effect of D-mannitol in the ink appears to be greater.

In the organic pigment of the present invention, most of the particles in the ink have a particle size of 0.1 μm or more and 1.0 μm or less, and an average particle size of 0.3 μm or more and 0.6 μm or less. Pigment. Pigment particles having a particle size of 0.1 μm or less are easy to secure stable dispersion, but are apt to cause stains. Particles having a particle size of 1.0 μm or more are difficult to generate stains but are difficult to secure stable dispersion. However, since a relatively small amount of such seed particles can be mixed, 5% by weight or less of pigment particles having a particle size of 0.1 μm or less and 1% or less of pigment particles having a particle size of
If it is 0% by weight or less, it can be sufficiently implemented. Organic pigments having such a particle size distribution can be easily realized by those skilled in the art by selecting the pigment synthesis stage and the subsequent process conditions of pulverization or ink formation.

The ink composition of the present invention is effective for various organic pigments, and is particularly effective for quinacridone pigments, perylene pigments, perinone pigments, diketopyrrolopyrrole pigments, polymer condensed azo pigments, isoindolinones. Pigments, imidazolone pigments, anthoraquinone pigments, dioxazine pigments, brominated phthalocyanine pigments, and the like. Azo pigments, disazo pigments, phthalocyanine pigments, chlorinated phthalocyanine pigments, thioindigo pigments and the like are effective but slightly inferior to the above-mentioned pigments. Although the reason is unknown, the factors affecting the dispersion state such as the electrical properties of the pigment surface, the specific gravity of the pigment, the number of fine particles due to the difficulty of pulverization by the pigment type are also related to stain at the same time I think that the.

In the ink of the present invention, the medium is water.
However, alcohols such as ethanol and isopropyl alcohol to enhance the quick drying of the ink, and polyhydric alcohols such as ethylene glycol and glycerin to ensure smooth writing and prevent solidification by drying the ink on the felt core Can be included in a small proportion. The aqueous medium in the present invention is water to which water and the above-mentioned hydrophilic medium are added. The type and amount of the hydrophilic medium to be added can be selected by a conventionally known technique from the viewpoint of the commerciality of the ink. Although the use of a hydrophilic medium enhances the usability of the pen and the ink, the dispersion stability of the pigment and the stain prevention performance tend to decrease, so that it is preferable to minimize the use. The amount of addition is roughly 1 at most with respect to 100 parts by weight of water.
It is better to use up to 0 parts by weight. It is advisable to avoid using ketones, which are hydrophilic media, from the viewpoint of the dispersion stability of the pigment.

The compounding ratio of the aqueous pigment ink for a white plate of the present invention is as follows in terms of parts by weight of each component in 100 parts by weight of the ink. The organic pigment is in the range of 1 part by weight or more and 6 parts by weight or less, and is selected according to the coloring property of the pigment.
Generally speaking, sufficient handwriting visibility is achieved with 3 parts by weight. Polyvinyl alcohol as a dispersant is one of the pigments
It is from / 6 to 1 part by weight, and 0.15 to 6 parts by weight in the ink. If the amount is less than this range, the dispersibility of the pigment in the ink cannot be ensured. If the amount is too large, the basic performance as a writing implement material is impaired, for example, the viscosity of the ink is high and the writability deteriorates. Preferably 0.5
Not less than 2.5 parts by weight. The release agent can be used in an amount equal to or more than 16 times by weight of the pigment. If the amount is less than this range, the effect of preventing stain cannot be exerted. If the amount is too large, the effect of preventing stain is saturated and waste of the release agent is lost. In addition, drawbacks appear in writability. Preferably, the amount is 3 to 6 times by weight of the pigment, and 10 to 15 parts by weight in the ink. The balance of the formulation described above is the aqueous medium.

The composition of the release agent contained in the above composition is such that the monoalkyl ether of polyoxyethylene glycol is at least 1/3 weight and at least 1 weight of the pigment and 0.7 to 5 parts by weight in the ink. Particularly preferably, it is 1 part by weight or more and 4 parts by weight. Alkylamine acetate is used in an amount of 1/3 to 3.5 times by weight of the pigment, preferably 0.7 to 15 parts by weight in the ink, and more preferably 4 to 15 parts by weight.
It is from 9 parts by weight to 9 parts by weight. D-mannitol is 以上 to 2.5 times the weight of the pigment, 1 to 10 parts by weight, particularly preferably 2 to 8 parts by weight in the ink. Even when the amount of each release agent used is outside the above range, an aqueous pigment ink can be obtained. However, if the amount is too small, the effect of preventing stain is not exhibited, and if it is too large, the writability deteriorates.

To the aqueous pigment ink for a white plate of the present invention, a preservative or the like is added as required in addition to the above components. The type and amount of addition can be selected by a conventionally known technique, and are at most about 1 part by weight or less in 100 parts by weight of the ink.

The aqueous pigment ink for a white plate of the present invention can be made into an ink by a series of methods, such as pulverization and dispersion, using the above-mentioned various components and conventionally known ones.

Hereinafter, the present invention will be described with reference to examples. Parts in the examples are parts by weight. The particle size distribution of the pigment was measured by applying the prepared ink to a laser diffraction type particle size distribution analyzer (manufactured by Shimadzu Corporation, SALD-1100). The viscosity of the aqueous solution of polyvinyl alcohol is a value measured at 20 ° C. using a B-type viscometer.

Example 1 3.0 parts of a perylene pigment, Pigment Red 149 (manufactured by Hoechst, PV Fast Red B), and a 4% aqueous solution having a viscosity of 30 c as a dispersant
ps, polyvinyl alcohol having a saponification degree of 88 mol% (Gosenol GH-1 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)
7) 1.0 part, 3.0 parts of polyoxyethylene monolauryl ether having a HLB value of 8 (Neugen ET-83, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a release agent, laurylamine acetate (Kao Corporation) Acetamine 24).
0 parts, 6.0 parts of D-mannitol (manufactured by Kao Corporation, D-mannitol), 0.3 parts of halogen-containing nitrogen-sulfur compound (manufactured by Takeda Pharmaceutical Co., Ltd., Sluroff 72N) as a preservative,
82.7 parts of water as an aqueous medium was mixed, pulverized and dispersed to prepare a red aqueous pigment ink. The pigment particles have an average particle size of 0.
The particles having a particle size of 45 μm, a particle size of 0.1 μm or less and a particle size of 1.0 μm or more were 1% by weight or less, and the dispersion was uniform and good. This ink was loaded on a felt pen and written on a ceramic white plate, a melamine resin white plate, and a polyester resin white plate. Writability was good and clear handwriting remained. Five minutes after writing, no stain remained after wiping with a cloth eraser. One day after writing, no stain remained after wiping with the cloth-made erasing tool. The ink was uniformly dispersed after leaving the ink at room temperature for one month, and the same writing and erasing tests were performed on a ceramic white plate, a melamine resin white plate, and a polyester resin white plate. With satisfactory results.

Comparative Example 1 The dispersant of Example 1 was replaced with 4
Example 1 except that 1.0 part of polyvinyl alcohol (Gosenol NL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) having a% aqueous solution witherability of 5.0 cps and a saponification degree of 98.5 mol% was changed. A red aqueous pigment ink was prepared in the same manner as described above. The particle size distribution of the pigment immediately after preparation was almost the same as in Example 1, and the dispersion state was uniform and good. This ink was loaded on a felt pen and written on a ceramic white plate, a melamine resin white plate, and a polyester resin white plate. It was possible to write smoothly, and writing 5
After a minute, the stain was not wiped off by wiping with a cloth eraser. One day after writing, no stain remained after wiping with the cloth eraser. However, over time, bright and smooth writing became impossible, and when the ink stored at room temperature was separately observed, aggregation of the pigment occurred and the dispersion state was deteriorated. In the ink having the composition of this comparative example, although the stain was prevented, the ink was unsuitable in terms of stable dispersion of the pigment.

Comparative Example 2 One of the release agents in Example 1
A red aqueous pigment ink was prepared in the same manner as in Example 1, except that 4.0 parts of laurylamine hydrochloride (Pharmin R24H, manufactured by Kao Corporation) was used instead of the seed laurylamine acetate. The particle size distribution of the pigment was the same as in Example 1, and the dispersion was uniform and good.
This ink was loaded on a felt pen and written on a ceramic white plate and a melamine resin white plate. Although it was possible to write smoothly, the line width of the handwriting shrank as the ink dried. Five minutes after writing, the cloth was wiped off with a cloth eraser, and all stains remained thin. One day after the writing, the stain was wiped off with a cloth eraser, and the stain remained thin. When the ink was observed at room temperature for one month, the dispersion state of the pigment was deteriorated. When the writing and erasing tests were performed on a ceramic white plate and a melamine resin white plate, both stains remained thin. The result was unsatisfactory.

(Example 2) 4.0 parts of Indanthrene pigment, Pigment Blue 60 (Fastgen Super Blue 6070S, manufactured by Dainippon Ink and Chemicals, Inc.), a kind of anthoraquinone pigment, as a dispersant Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., Kuraray Povar PV) having a 4% aqueous solution viscosity of 5.0 cps and a saponification degree of 88 mol%
A-205) 1.5 parts, 2.0 parts of a polyoxyethylene monolauryl ether having a HLB value of 8 (Neugen ET-83, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a release agent, stearylamine acetate (Kao ( Acetamine 8
6) 7.0 parts, D-mannitol (manufactured by Kao Corporation, D-mannitol)
2.0 parts of mannitol, a halogen-containing nitrogen-sulfur compound as a preservative (Takeda Pharmaceutical Co., Ltd., Slaoff 72N)
0.3 parts, 83.2 parts of water as an aqueous medium were mixed and pulverized,
This was dispersed to prepare a blue aqueous pigment ink. The pigment had an average particle size of 0.50 μm, and particles having a particle size of 0.1 μm or less and 1.0 μm or more were both 1% by weight or less, and the dispersion state was uniform and good. This ink was loaded on a felt pen and written on a ceramic white plate, a melamine resin white plate, and a polypropylene resin white plate. Writability was good and clear handwriting remained. Five minutes after writing, the stain was not wiped off with a soft paper. One day after the writing, the stain was not wiped off with the soft paper. In addition, the dispersion of the pigment was uniform and good even after leaving this ink at room temperature for one month.
The same writing and erasing tests as above were performed on three types of white board with similar satisfactory results.

Comparative Example 3 One of the release agents in Example 2
In place of the species polyoxyethylene monolauryl ether,
Polyoxyethylene monononyl phenyl ether having an HLB value of 8 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Neugen EA-
70) A blue aqueous pigment ink was prepared in the same manner as in Example 2, except that 2.0 parts was used. The particle size distribution of the pigment was the same as in Example 2, and the dispersion was uniform and good. Load this ink into a felt pen,
Writing was performed on a ceramic white plate, a melamine resin white plate, and a polypropylene resin white plate. Although writing was possible smoothly, the line width of the handwriting shrank as the ink dried. Five minutes after writing, the sheet was wiped with a soft paper, but a thin stain remained.
One day after writing, it was wiped off with a soft paper, but a thin stain remained. When this ink was observed after standing for one month, the dispersion state of the pigment was deteriorated. The writing and erasing tests were performed on a ceramic white plate, a melamine resin white plate, and a polypropylene resin white plate. It was a good result.

Comparative Example 4 One of the release agents in Example 2
In place of the species polyoxyethylene monolauryl ether,
A blue aqueous pigment ink was prepared in the same manner as in Example 2, except that 2.0 parts of triethylene glycol monoethyl ether was used. The particle size distribution of the pigment was the same as in Example 2, and the dispersion was uniform and good.
This ink was loaded on a felt pen and written on a ceramic white plate, a melamine resin white plate, and a polypropylene resin white plate. Although writing was possible smoothly, the stain was left after wiping with soft paper 5 minutes after writing. One day after writing, it was wiped off with a soft paper, but a thin stain remained.

Example 3 Pigment Green 36, a brominated phthalocyanine pigment (Toyo Ink Manufacturing Co., Ltd.)
5.0 parts of a 4% aqueous solution having a viscosity of 5.0 cps as a dispersant and a saponification degree of 79 mol% (Gosenol KL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) 2.0 parts, polyoxyethylene monoalkyl ether having an HLB value of 9 as a release agent (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Neugen ET-
97) 4.0 parts, laurylamine acetate (manufactured by Kao Corporation, acetamine 24) 9.0 parts, mannitol (manufactured by Kao Corporation, D-mannitol) 4.0 parts, halogen-containing sulfur-containing preservative Compound (Takeda Pharmaceutical Co., Ltd.)
0.3N, water 7 as an aqueous medium
0.7 parts and 5.0 parts of ethanol were mixed, pulverized and dispersed to prepare a green aqueous pigment ink. The average particle size of the pigment is 0.
The content of particles having a particle size of 35 μm and a particle size of 0.1 μm or less was 0.5% by weight or less, and the content of the particles having a particle size of 1.0 μm or more was 3.5% by weight. This ink was loaded on a felt pen and written on a ceramic white plate and a melamine resin white plate. Writability was good and clear handwriting remained. Five minutes after writing, no stain remained after wiping with a felt eraser. One day after writing, no stain remained after wiping with a felt eraser. In addition, the dispersion of the pigment in the ink is uniform and good even after being left for one month,
When the same writing and erasing tests as described above were performed on a ceramic white board and a melamine resin white board, satisfactory results were obtained with no stain remaining.

(Comparative Example 5) 1 of the release agent in Example 3
A green aqueous pigment ink was prepared in the same manner as in Example 3, except that 4.0 parts of soluble starch (Stabilose K, manufactured by Matsutani Chemical Industry Co., Ltd.) was used instead of seed D-mannitol. . The particle size distribution of the pigment was the same as in Example 3, and the dispersion of the pigment was uniform and good. This ink was filled in a felt pen and written on a ceramic white plate and a melamine resin white plate. Writability was good and clear handwriting remained. Five minutes after writing, no stain remained with the felt erasing tool. However, one day after writing, an attempt was made to wipe it off with a felt eraser, but the stain remained thin. In addition,
Observation of this ink after standing for one month revealed that the dispersion state of the pigment had deteriorated. Writing and erasing tests were performed on a ceramic white plate and a melamine resin white plate. After 5 minutes of writing, a felt erasing tool was used. No wiping stain remained, but one day after writing, the stain remained thin.

(Comparative Example 6) 1 of the release agent in Example 3
A green aqueous pigment ink was prepared in the same manner as in Example 3, except that 9.0 parts of an equimolar salt of ethylamine and acetic acid was used as a salt instead of 9.0 parts of seed laurylamine acetate. did. The particle size distribution of the pigment was almost the same as in Example 3, and the dispersion of the pigment was uniform and good.
This ink was loaded on a felt pen and written on a ceramic white plate and a melamine resin white plate. Writability was good and clear handwriting remained. Five minutes after writing, the cloth was wiped off with a felt eraser, and stains remained. One day after writing, an attempt was made to wipe it off with a felt eraser, but stain remained.

[0029]

According to the present invention, in an ink in which an organic pigment, a dispersant, and a release agent are dispersed in an aqueous medium as essential components, an organic pigment having a specific particle size distribution is used, and polyvinyl alcohol having a specific molecular weight and a degree of saponification is used as a dispersant. Is excellent in dispersion stability by using a polyoxyethylene glycol monoalkyl ether having a specific HLB value and a specific alkylamine acetate and D-mannitol as a release agent, so that no trace of ink remains upon erasing. It has become possible to provide an aqueous pigment ink for a white plate.

Claims (3)

[Claims] 1. An ink in which an organic pigment, a dispersant, and a release agent are dispersed in an aqueous medium as essential components, the viscosity of a 4% aqueous solution as a dispersant is 3 cps to 60 cps, and the degree of saponification is 70 mol%. A polyoxyethylene glycol monoalkyl ether having an alkyl group having 6 to 22 carbon atoms and an HLB value of 6 to 10 as a releasing agent,
An aqueous pigment ink for a white plate, characterized by using an alkylamine acetate having an alkyl group having 8 to 20 carbon atoms and D-mannitol. 2. A compounding ratio of each component is 72 to 92 parts by weight of an aqueous medium, 1.0 to 6.0 parts by weight of an organic pigment, and 0.15 parts by weight or more of a dispersant in 100 parts by weight of an ink. 6.0 parts by weight or less, release agent 6.0 parts by weight or more 1
6 parts by weight or less, and the compounding ratio of each release agent to the pigment to be used is such that the monoalkyl ether of polyoxyethylene glycol is at least 1/3 weight and at most 1 weight, and the alkylamine acetate is 1/3. The aqueous solution for a white board according to claim 1, wherein the weight ratio is not less than 3.5 times by weight and D-mannitol is a ratio selected from the range of 1/2 times to 2.5 times by weight. Pigment ink. 3. An organic pigment having an average particle size in an ink of 0.1.
2. The method according to claim 1, wherein the particle size is in the range of 3 μm to 0.6 μm, and the particles having a particle size of 0.1 μm or less are 5% by weight or less and the particles having a particle size of 1 μm or more are 10% by weight or less. The aqueous pigment ink for a white plate as described in the above.