JP2003171593A - Water-based ink composition for writing tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a water-based ink composition for a writing tool suppressed enough in sedimentation of matters having a high specific gravity such as a pigment and the like in an ink composition to dispense with agitation for redispersion and also suppressed in sedimentation of a pigment when a pigment having a relatively high specific gravity is used or an ink for a writing tool having a low viscosity is used. <P>SOLUTION: The water-based ink composition for a writing tool contains a specific amount of at least one specific gravity-regulating agent selected from a polymolybdate salt and a polytungstate salt. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to suppression of sedimentation of a pigment in an aqueous ink composition for writing instruments. Further, the present invention relates to a water-based ink composition for a writing instrument that can suppress the sedimentation of the pigment even when a pigment having a relatively high specific gravity is used or a low viscosity ink for a writing instrument is used.

[0002]

2. Description of the Related Art In a conventional writing ink, when a pigment having a large difference in specific gravity from an ink medium is used in a low-viscosity writing ink, the pigment is settled and it cannot be prevented. For example, an ink having a metallic luster color as proposed in JP-A-61-23684 and JP-A-63-95277 usually uses a metal powder pigment having a large specific gravity, but the ink itself. However, there is a problem in the ink stability such that the pigment is precipitated and separated due to its low viscosity. Further, even in a white ink for obtaining white handwriting having a hiding power, when titanium oxide having a large specific gravity is used as a pigment because it has a hiding power, it is difficult to stably disperse it in a low-viscosity ink, and oxidation occurs over time. There was a problem that titanium would settle. These low-viscosity inks that have a metallic luster color or white contain a stirring member such as a metal ball in the ink chamber, and you can obtain good handwriting unless you shake the writing instrument and redisperse the pigment that settled out before use. A writing instrument that uses a pen body that utilizes the capillary phenomenon, such as a fountain pen, felt-tip pen, marking pen, plate pen, etc., and has no valve mechanism between the ink storage chamber and the pen body. However, there was a fatal drawback that it could not be used.

On the other hand, JP-A-7-145339, JP-2978798, and JP-A-2001-29479.
As described in Japanese Patent Publication No. 5, the addition of natural polysaccharides such as guar gum and xanthan gum, and synthetic thickeners such as cross-linked acrylic acid polymer causes shear thinning of the ink, resulting in high viscosity at rest. Also known is a method of suppressing the sedimentation of the pigment. However, although the ink obtained by this method does not require a stirring member such as a metal ball, the pigment still slowly settles down or the use of a pigment having a large specific gravity is limited. In addition, since it has a shear thinning property, it has a high viscosity at low shear, and it is required to follow the ink without applying much shear.For example, a fountain pen, felt-tip pen, marking pen, plate pen, etc. Ink was adopted, and it could not be used for a writing instrument with a writing instrument mechanism that utilizes the capillary phenomenon.

Further, as a method for suppressing the sedimentation of the pigment, a method is known in which a pigment having a low specific gravity is adopted to reduce the difference in specific gravity between the ink medium and the pigment. in this way,
It is necessary to select a pigment that has a particularly low specific gravity for the ink medium that uses water as the main solvent, and it is difficult to minimize the difference in the specific gravity between the ink medium and the pigment. It could not be prevented. For example, Japanese Patent Application Laid-Open No. 49-31428 proposes an ink using a metal vapor deposition powder having a specific gravity smaller than that of aluminum as a pigment of a writing instrument ink having a metallic luster color. However, although it is a material having a lower specific gravity than aluminum, it has a higher specific gravity than general pigments, and pigment settling cannot be suppressed even as a low-viscosity ink for use in a writing instrument mechanism utilizing the capillary phenomenon. It was a thing. Furthermore, if a particle having a relatively large particle size is used in order to obtain a handwriting with a sufficient metallic luster color, it becomes difficult to obtain the effect of dispersion stabilization due to Brownian motion, and thus it becomes more difficult to suppress the sedimentation of the pigment. There was also a problem with the conflicting requirements.

Further, Japanese Patent Application Laid-Open No. 9-221617 proposes an ink using a white plastic pigment having a smaller specific gravity than titanium oxide as a pigment of a white ink for writing a white handwriting. However, the sedimentation stability of the white plastic pigment is said to be obtained by including a viscosity modifier in the ink and adjusting the ink viscosity at a shear rate of 3.84 s ^{−1 to} a specific range of 100 to 2000 mPa · s. As described above, it is possible to use an ink having a shear thinning property, and it is not possible to suppress the sedimentation of the pigment even as a low-viscosity ink for use in a writing instrument mechanism utilizing a capillary phenomenon.

By the way, JP-A-60-115674, JP-A-64-40583 and JP-A-10-21
Japanese Patent No. 9177 and Japanese Patent Laid-Open No. 11-228900 disclose inks containing molybdate or tungstate added to inks for writing instruments. JP-A-60
In JP-A-115674 and JP-A-64-40583, as a lubricant in an ink for water-based ballpoint pens,
Further, JP-A-10-219177 and JP-A-11-
In JP-A-228900, molybdates and tungstates are added as corrosion inhibitors in aqueous inks for ballpoint pens. However, neither is added for the purpose of adjusting the specific gravity of the ink medium, and the effect thereof is not described at all. Furthermore, the amount of molybdate or tungstate added is 4.9% by mass (5.0% by weight) or less, and 7.
84 mass% (8 wt%) or less or 9.8 mass% (1
However, the effect as a specific gravity adjusting agent cannot be expected by adding such a small amount, and there is no suggestion.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a water-based ink composition for a writing instrument which suppresses sedimentation of the pigment in the water-based ink composition for a writing instrument and does not require stirring for redispersion. It is an object of the present invention to provide a water-based ink composition for a writing instrument that can suppress the sedimentation of the pigment even when a pigment having a relatively high specific gravity or a low-viscosity writing ink is used. It proposes a solution to such a problem.

[0008]

In order to solve the above-mentioned problems, the present invention aims to solve the above-mentioned problems by adding a specific gravity adjusting agent to the ink medium to reduce the difference in specific gravity between the ink medium and the pigment. A water-based ink composition for writing instruments was completed. That is, the present invention provides "1. A water-based ink composition for a writing instrument, which contains at least a specific gravity adjusting agent, a pigment, and water, and the specific gravity adjusting agent is at least one selected from polymolybdate and polytungstate. 2. The water-based ink composition for a writing instrument according to item 1, wherein the specific gravity adjusting agent is sodium metatungstate 3. The blending amount of the specific gravity adjusting agent is 10.0 to 80.0 mass with respect to the entire ink composition. The water-based ink composition for a writing instrument according to any one of the items 1 and 2, which is% .4. Any one of the items 1 to 3 wherein the specific gravity of the pigment is 1.2 to 3.1. The water-based ink composition for a writing instrument according to item 1. 5. Any of items ¹ to 4, wherein the viscosity of the ink composition at a shear rate of 384 s ⁻¹ (at 20 ° C.) is 2.0 to 100.0 mPa · s. Writing described in paragraph 1 Water based ink composition. "A.

According to the above water-based ink composition for a writing instrument,
It suppresses the sedimentation of the pigment in the ink composition, does not require stirring for redispersion, and causes the sedimentation of the pigment when using a pigment having a relatively high specific gravity or when using a low-viscosity writing ink. It is possible to obtain an excellent effect of being able to suppress.

The specific gravity adjusting agent used in the present invention is at least one selected from polymolybdate and / or polytungstate. The polymolybdate and polytungstate in the present invention also include respective isopolyacid and heteropolyacid salts. Polyacid is a multiple acid produced by condensation of oxyacids of metal elements such as molybdenum and tungsten.A polyacid composed of only one type of metal is called isopolyacid.Isopolyacid and oxyacids of other elements are The condensed polyacid is called a heteropolyacid. Specific examples of the isopolyacid salt include ammonium paramolybdate, sodium metatungstate, and ammonium metatungstate.
Specific examples of the heteropolyacid salt include sodium molybdophosphate, sodium molybdosilicate, sodium tungstophosphate, and sodium tungstosilicate. These polymolybdates and polytungstates can be used alone or in admixture of two or more.

These specific gravity adjusting agents are added for the purpose of adjusting the specific gravity of the ink medium to the specific gravity of the pigment by being dissolved in the ink medium. Therefore, the addition amount thereof depends on the specific gravity of the pigment used. The solubility can be arbitrarily set. In order to obtain a sufficient effect of suppressing sedimentation, it is preferable to add about 10.0 to 80.0% by mass, more preferably about 15.0 to 75.0% by mass, based on the entire ink composition. Below this range, the effect of adjusting the specific gravity of the ink medium tends to be poor, and when a pigment having a large specific gravity is used, a sufficient sedimentation suppressing effect cannot be obtained. On the other hand, the upper limit of the addition amount depends on the solubility of the specific gravity adjusting agent used. The one having a higher solubility in water can correspond to pigments having various specific gravities and is preferably used as a specific gravity adjusting agent. Further, as the added amount increases and the concentration becomes higher, the viscosity of the solution increases, so that it must be appropriately adjusted depending on the combination of the specific gravity adjusting agent and the writing instrument used. The ink medium used in the present invention is the rest of the composition obtained by removing the pigment component from the aqueous ink composition for writing instruments.

The specific gravity of the ink medium depends on the specific gravity of the water-soluble substance dissolved in the ink medium and the amount added. The specific gravity of the ink medium can be increased by adding a large amount of a water-soluble substance having a large specific gravity to the ink medium and dissolving it. Since polymolybdate and polytungstate contain a metal element having a high specific gravity such as molybdenum and tungsten and are compounds having a relatively large specific gravity, they are preferably used as an additive for adjusting the specific gravity of the ink medium. You can It is considered that the specific gravity adjusting agent usefully acts because the specific gravity adjusting agent itself has a large specific gravity and is water-soluble, and this is presumed to be the mechanism for adjusting the specific gravity in the aqueous ink composition for a writing instrument of the present invention.

In the case of the present invention, heavy metal elements such as molybdenum and tungsten are required to increase the specific gravity. Molybdenum has a specific gravity of 10.28 and tungsten has a specific gravity of 1.
It is 9.32. Among them, sodium metatungstate has a very high solubility in water, and the specific gravity of the aqueous solution thereof can be freely set within the range of 1.0 to 3.1, and therefore it can be suitably used as a specific gravity adjusting agent.

The sedimentation stability of the pigment becomes maximum when the difference in specific gravity between the ink medium and the pigment is minimal. However, it should be noted that the specific gravity of the pigment in the ink composition may be different from the true specific gravity. This is because the apparent specific gravity of the pigment changes due to the influence of other additives in the ink composition in addition to the structure of the pigment itself. It is different for each. Therefore, the specific gravity of the ink medium needs to be adjusted for each composition of the ink composition so that the sedimentation stability of the pigment becomes the best.

By the way, no attempt has been made to prevent the sedimentation of the pigment by increasing the liquid specific gravity of the ink medium as an ink composition, but generally, a method for increasing the liquid specific gravity of a solution is used in other industries. Was used. However, the technique is based on bromoform, tetrabromoethane,
The ones that use specific gravity adjusting agents such as methylene iodide, and those that use carcinogenic substances containing toxic halogen elements and toxic heavy element ions and having stimulant and anesthetic properties were the mainstream. Such a specific gravity adjusting agent could not be used very much in the ink for writing instruments as general daily necessities which are not used in the specialized industrial field.

The polymolybdenum compound and polytungsten compound used in the present invention are generally compounds having low toxicity. Molybdenum is also present in the human body and is an essential element for animal survival. Tungsten has the highest boiling point among many heavy metals, and the element that is generally harmful to the human body has a lower boiling point, and is considered to be a relatively safe metal. In particular, sodium metatungstate is a highly safe compound and is preferable, as reported in Geologic News No. 455, page 31, as being nontoxic. In this way, by using polymolybdate and polytungstate, which are very stable substances, it is possible to obtain an aqueous solution which is non-toxic to the human body and has a high specific gravity, and a pigment having a relatively high specific gravity was used. It is extremely suitable for use as an additive for a water-based ink composition for writing instruments.

The pigment used in the present invention is not particularly limited as long as it has no chemical influence such as reaction with a specific gravity adjusting agent. For example, organic pigments and plastics usually used for writing instrument inks. In addition to pigments and inorganic pigments, metal powder pigments having metallic luster, colored metal powder pigments, metal vapor deposition powder pigments, pearl pigments having a color such as glass flakes and iris colors, and cholesteric liquid crystals are listed. Among them, when a high specific gravity pigment having a specific gravity of about 1.2 to 3.1 is used, it works particularly effectively.

Specific examples of the organic pigments include Hansa Yellow, Benzidine Yellow, Permanent Red, Lake Red, Victoria Blue Lake, Phthalocyanine Blue, Phthalocyanine Green, and Aniline Black. The specific gravity is approximately 1.2 to 2.9.

It is preferable to use a plastic pigment having a relatively low specific gravity such that white or colorful pigments can be selected because the burden on the specific gravity adjusting agent is reduced. Some processed pigments have a low specific gravity, and when such pigments are used, it is possible to increase the blending amount of the pigment itself and to obtain an ink composition with higher dispersion stability. so,
It is also very effective when used in combination with a pigment whose specific gravity is lightened by processing. Plastic pigments include Lowpaque OP-62, OP-84J, OP-91, and HP.
1055 (above, manufactured by Rohm and Haas), Epocolor FP-1000N, FP-112, FP-1
13, same FP-114, same FP-115, same FP-11
6, the same FP-117, the same FP-101, the same MA-100
2FW, same FP-1050 (above, Nippon Shokubai Co., Ltd.), Lumicor NKP-8604, same NKP-860
5, the same NKP-8607, the same NKP-9203, the same NK
P-9207, NKP-9237, NKP-923
8 (above, manufactured by Nippon Fluorescent Chemical Co., Ltd.) and the like.
The specific gravity is approximately 1.0 to 1.4. Further, not only the processed pigment but also the pigment having a low specific gravity from the beginning can similarly improve the dispersion stability of the pigment by using the specific gravity adjusting agent of the present invention together.

Examples of the inorganic pigment include carbon black, ultramarine blue, various titanium oxides such as rutile type and anatase type. The specific gravity is about 1.
4 to 5.5, and various titanium oxides are about 3.7 to 4.2.

The commercially available titanium oxides are Tytone SR-1, R-650, R-3L and A-1.
10, the same A-150 (above, Sakai Chemical Industry Co., Ltd.), Taipaque R-580, the same R-550, the same R-780 (above, Ishihara Sangyo Co., Ltd.), Kronos KR-310, the same K.
R-380, KR-480, KA-10, KA-
15 (above, manufactured by Titanium Industry Co., Ltd.), TYPURE R-
900, R-931, R-960 (above, manufactured by DuPont Japan Limited), Titanics JR-3
01, the same JR-600A, the same JR-603, the same JA-4
(Above, manufactured by Teika Co., Ltd.) and the like. Also, L
IOFAST WHITE H201, EM WHITE
H, EM WHITE FX9048 (above, Toyo Ink Co., Ltd.), Pollux White PC-CR (Sumitomo Color Co., Ltd.), FUJI SP WHITE 11, 1
Use of commercially available titanium oxide aqueous dispersions such as 011, 1036, and 1051 (all manufactured by Fuji Dye Co., Ltd.) is preferable because the dispersion step in terms of production can be omitted and ink can be easily formed.

Titanium oxide is one of the pigments having a high specific gravity among various pigments, but the aqueous ink composition for a writing instrument of the present invention can obtain a certain degree of dispersion stability even in a low viscosity ink.

As the metal powder pigment, aluminum paste, aluminum powder, bronze powder, copper powder, zinc powder and the like are used. The specific gravity is approximately 2.5 to 9.0.

Since the aluminum paste is made by grinding and polishing aluminum metal powder in a ball mill containing mineral spirit and stearic acid or oleic acid to form very thin scale-like aluminum fine particles, there is a risk of ignition and explosion. There is little, and it is easy to handle in use. As a commercially available aluminum paste, Super Fine No. 22000 WN, the same No.
18000 WN (above, Daiwa Metal Powder Co., Ltd.), W
B0230 (manufactured by Toyo Aluminum Co., Ltd.), 400S
W, 010WD, FM4010WG (these are manufactured by Showa Aluminum Powder Co., Ltd.) and the like.

As aluminum powder, AA12, A
A8, No. 900, No. 18000 (above, manufactured by Fukuda Metal Foil & Powder Co., Ltd.).

Colored metal powder pigments include F503RG,
F503BG, F500SI, F500RE, F500
RE, F500BL (Showa Aluminum Powder Co., Ltd.)
Manufactured) and the like.

As the metal-deposited powder pigment, aluminum is vacuum-deposited on a synthetic resin, the metal layer is protected by the resin, and crushed into pieces in a state of LJ Silver # 500, # 32.
5, the same # 200 (above, manufactured by Oike Industry Co., Ltd.) and the like. In addition, the resin layer colored ELGE R. Gol
d # 500, ibid. Gold # 500, R.G. Gold
# 325, B. Gold # 325 and Red # 32
5, same Blue # 325, same Green # 325, same V
iolet # 325, Black # 325, and Cop
per # 325 and R.I. Gold # 200, B.I. Go
ld # 200, Red # 200, Blue # 20
0, Green # 200, Violet # 200,
Examples thereof include Black # 200 and Copper # 200 (all manufactured by Oike Kogyo Co., Ltd.). Such a processed pigment has a relatively low specific gravity and is approximately 1.2 to 1.3.
Is the specific gravity of.

As the glass flake pigment, metashine REFSX-2015PS, the same-2025PS, the same-a glass flake coated with a metal by an electroless plating method is used.
2040PS, RCFSX-5030NS, and -503
0NB, same-5030PS, same-2015PS, same-5
090GG (Nippon Sheet Glass Co., Ltd.), etc.
The specific gravity is approximately 3.0 to 3.4.

As the pearl pigment, Iriodin 120 is used.
Luster Satin and 123 Bright Lu
star Satin, same 201 Rutile Fin
e Gold and 211 Rutile Fine Re
d, 221 Rutile Fine Blue, 2
23 Rutile Fine Lilac, 231 R
utile Fine Green, 302 Gold
Satin, 323 Royal Gold Sati
n, same 520 Bronze Satin, same 522 R
ed Brown Satin, 524 Red Sat
in (above, manufactured by Merck Japan Ltd.) and the like, and the specific gravity thereof is about 3.0.

Cholesteric liquid crystals include helicone HC SLM90020, 90120, 9022.
0 and 90320 (above, manufactured by Wacker Chemie), etc., and the specific gravity is about 1.3.

Even if these pigments are used alone, 2
You may use it in combination of 2 or more types. Further, pigments or dyes having a small specific gravity may be used in combination within a range that does not affect the stability. Furthermore, dyes that are not completely soluble in water can also be used because they can obtain the effect of suppressing sedimentation as with pigments. The addition amount of these pigments and / or dyes is not particularly limited as long as a sufficient concentration can be obtained as a water-based ink composition for writing instruments. Further, the particle diameters of these pigments and / or dyes are not particularly limited as long as they are within the range adapted to the pen body of the writing instrument to be used.

The water-based ink composition for a writing instrument of the present invention is useful in any form of ink composition such as Newtonian ink and shear thinning ink, but the lower viscosity ink is a pigment or other dispersion. It is more preferably used because it has a large problem of sedimentation. Shear rate 384s
The viscosity of the ink composition at ^-1 (at 20 ° C) is 2.0.
In the case of an ink composition of 100.0 mPa · s, a larger effect can be obtained.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a specific gravity adjusting agent, a pigment and water are essential components, but components other than these components which are usually used as an ink composition for writing instruments can also be optionally used. For example, a resin or the like usually used for adjusting the ink viscosity or improving the fixability of the pigment to the writing medium and the water resistance may be added. Further, components such as antiseptics, rust preventives, dispersants, lubricants, humectants, pH adjusters, viscosity adjusters, shear thinning agents, and surfactants can also be used. However, the kind and the addition amount thereof must be used within a range that does not affect the specific gravity adjusting function of the specific gravity adjusting agent used in the present invention.

As the preservative, 1,2-benzisothiazolin-3-one, sodium benzoate and the like can be used.

As moisturizers, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, hexylene glycol, glycerin and polyethylene glycol, urea and the like may be used alone or in combination of two or more kinds. can do.

As the pH adjuster, monoethanolamine, diethanolamine, triatanolamine, N,
N-diethanolamine, N, N-dibutylethanolamine, N, N-methyldiethanolamine, sodium hydroxide, potassium carbonate and the like can be used.

As the shear thinning agent, it is possible to use a shear thinning agent such as an inorganic type, a natural polymer type, a synthetic polymer type or a polymer polysaccharide type.

The aqueous ink composition for a writing instrument of the present invention can be produced by various known methods for producing an ink composition for a writing instrument. The aqueous ink composition for a writing instrument of the present invention can be suitably used for fountain pens, felt-tip pens, marking pens, plate pens, ball-point pens and the like.

[0039]

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the examples.

Example 1 Moisturizer (Note 1) 25.0 parts by mass Moisturizer (Note 2) 6.3 parts by mass Dispersant (Note 4) 1.0 part by mass Lubricant (Note 5) 0.5 parts by mass Preservative (Note 6) 0.2 parts by mass pH adjuster (Note 7) 1.0 parts by mass Pigment (Note 8) 20.0 parts by mass Ion-exchanged water 46.0 parts by mass Sodium metatungstate (specific gravity modifier) 18.0% by mass First, after dissolving the specific gravity adjusting agent in ion-exchanged water, components other than the pigment are mixed, and a considerable amount of the pigment is added to the mixture with stirring to obtain a metallic luster color. An aqueous ink composition for a writing instrument was obtained. As the specific gravity adjusting agent, sodium metatungstate SPT (manufactured by SOMETU) was used. As a dispersant, polyvinylpyrrolidone (K-1
5 ISP Technologies) was used. As a lubricant, a phosphate ester type surfactant (Prysurf A-2
08S Daiichi Kogyo Seiyaku Co., Ltd. was used. As the preservative, 1,2-benzisothiazolin-3-one (Proxel XL-2 (S) manufactured by Avicia Co., Ltd.) was used. pH
Triethanolamine was used as a regulator. As the pigment, a metal vapor-deposited powder pigment (ELGI Silver # 500
Oike Industry Co., Ltd. was used.

Examples 2 to 11 Water-based ink compositions for writing instruments were obtained in the same manner as in Example 1 except that the ink composition was as shown in Table 1. Example 2
4 to 9 to 11 are water-based ink compositions for writing instruments that give metallic glossy handwriting, and Examples 5 to 8 are aqueous ink compositions for white writing instrument.

Comparative Examples 1 to 7 Water-based ink compositions for writing instruments were obtained in the same manner as in Example 1 except that the ink composition was as shown in Table 2. Comparative Examples 1, 2, 5 and 7 are water-based ink compositions for writing instruments that obtain metallic glossy handwriting, and Comparative Examples 3 and 4 are white ink-based aqueous ink compositions for writing instruments.

[0043]

[Table 1]

[Table 2] Note 1: Ethylene glycol Note 2: Urea Note 3: Glycerin Note 4: Polyvinylpyrrolidone (K-15 ISP Technologies) Note 5: Phosphate ester surfactant (Prysurf A-
208S Dai-ichi Kogyo Seiyaku Co., Ltd. Note 6: 1,2-Benzisothiazolin-3-one (Proxel XL-2 (S) Abyssia Ltd.) Note 7: Triethanolamine Note 8: ERGI Silver # 500 (Oike Industry Co., Ltd.
Manufactured), specific gravity 1.2 to 1.3 Note 9: ELG R. Gold # 500 (Oike Industry Co., Ltd.)
Made), specific gravity 1.2 to 1.3 Note 10: FM4010WG (Showa Aluminum Powder Co., Ltd.)
, Specific gravity around 2.5 Note 11: Epocolor MA-1002FW (manufactured by Nippon Shokubai Co., Ltd.), specific gravity 1.2 to 1.3 Note 12: Taitone A-110 (Sakai Chemical Industry Co., Ltd.)
, Specific gravity of around 3.9 * 13: Hibiswako 105 (Wako Pure Chemical Industries, Ltd.)
Note 14: SPT (manufactured by SOMETU) Note 15: n-hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) Note 16: 1 grade (manufactured by Kanto Chemical Co., Inc.)

In the above Examples 1 to 11 and Comparative Examples 1 to 7,
The ink composition obtained was tested by the following test method.
Test was carried out. The results are shown in Tables 1 and 2. 1. Specific gravity of ink medium: Remove only pigment from ink composition
The specific gravity of the ink medium blended is 10 at 20 ° C.
It measured using the ml specific gravity bottle. 2. Floating / sedimentation stability of pigment: Ink composition
Fill and seal the ink cartridge for fountain pen made by Ylot.
After leaving it in a vertical position for a certain period of time, the pigment is dispersed.
The state was visually confirmed. Evaluation criteria are as follows:
It was evaluated. ⊚: The pigment was stable for 2 weeks or more. ◯: The pigment was stable for 1 week. Δ: The pigment was stable for 3 days. X: The pigment was not stable for 6 hours. 3. Ink viscosity: DV-2 + viscosity after making the ink composition
Total (Brookfield), CPE-42 Spind
Using a shear rate of 384s^-1(100 rpm)
Viscosity was measured (at 20 ° C.). Ink viscosity is 6
If it exceeds 4.0 mPa · s, with DV-2 + viscometer
Stress controlled rheometry because it cannot be measured with
Using a CSL-100 (caliber), diameter 4c
shear rate of 3 using a cone plate (2 °)
84s^-1Was measured (at 20 ° C.).
(Comparative Example 7) Furthermore, in Example 8, 3.84s
^-1The viscosity at (1.0 rpm) was also measured.

From the results shown in Table 1, the aqueous ink compositions for writing instruments of Examples 1 to 11 can be suitably used for fountain pens, felt-tip pens, marking pens, plate pens, ballpoint pens, etc., and Examples 1 to 7 and 9 to 11 It can be seen that the above example is an excellent ink composition having a low viscosity but good sedimentation stability of the pigment and not requiring stirring for redispersion.
In particular, in Examples 2 and 4, a very good evaluation can be obtained, and in Example 2, good ink stability can be obtained while having an extremely low viscosity, and a variety of writing mechanisms to be used can be widened. did it. Although Example 8 is a shear thinning ink, the stability of the pigment could be improved. Examples 3, 5, and 9 had a slightly settling tendency, and Examples 7 and 11 had a slightly floating tendency, but were at a usable level.

Although it was not listed as an example because of its difficulty in reacting with the lubricants and dispersants listed in the examples, even if sodium molybdophosphate is used, another lubricant or dispersant can be appropriately selected. A good water-based ink composition for writing instruments could be obtained.

Further, as shown in Table 2, Comparative Examples 1 to 4
In the above, since no specific gravity adjusting agent was blended, the pigment settled insufficient even if any pigment was used. In Comparative Example 5, the addition amount of the specific gravity adjusting agent was small, and the effect of suppressing the sedimentation of the pigment was insufficient. In Comparative Example 6, the addition amount was too large because the specific gravity adjusting agent having poor solubility in water was used. It could not be completely dissolved. In Comparative Example 7, although the viscosity was increased and the sedimentation of the pigment was delayed, the sedimentation could not be basically prevented, and the viscosity was too high when used as a low viscosity writing ink, which was not preferable.

[0048]

As is apparent from the above description, the aqueous ink composition for a writing instrument of the present invention suppresses the sedimentation of the pigment in the ink composition by using a specific gravity adjusting agent, etc. An aqueous ink composition for a writing instrument that does not require stirring for dispersion and can suppress the sedimentation of the pigment even when using a relatively high specific gravity pigment or when using a low viscosity writing instrument ink It is possible to achieve an excellent effect. Further, not only the pigment but also the dispersion of high specific gravity in the ink composition can be stabilized, which is very useful.

Claims (5)

[Claims] 1. An aqueous ink composition for a writing instrument, which contains at least a specific gravity adjusting agent, a pigment and water, and the specific gravity adjusting agent is at least one selected from polymolybdate and polytungstate. 2. The water-based ink composition for a writing instrument according to claim 1, wherein the specific gravity adjusting agent is sodium metatungstate. 3. The water-based ink composition for a writing instrument according to claim 1, wherein the blending amount of the specific gravity adjusting agent is 10.0 to 80.0 mass% with respect to the entire ink composition. . 4. The aqueous ink composition for a writing instrument according to claim 1, wherein the specific gravity of the pigment is 1.2 to 3.1. 5. The viscosity of the ink composition at a shear rate of 384 s ⁻¹ (at 20 ° C.) is 2.0 to 100.0 mPas.
The water-based ink composition for a writing instrument according to any one of claims 1 to 4, which is s.