JP2002363468A - Ink composition for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare an ink that can continue stabilized ink jetting because it has excellent clogging resistance, even after continuous printing for a long time, further attains excellent quality of printed matters with excellent water resistance, rubbing resistance and quick drying properties. SOLUTION: The ink composition for ink-jet recording includes at least one selected from a water-soluble organic solvent comprising tertiary butyl alcohol, neopentyl alcohol, N-methyl-pyrrolidone, diethylene glycol and polyethylene glycol, pigments and a water-soluble resin and the remaining is water. In this case, the amount of the water-soluble organic solvent is characteristically 3-40 wt.%, the pigment is 0.1-20 wt.% and the water-soluble resin is 0.1-5 wt.% on the basis of the whole weight of the ink composition, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ink composition for ink jet recording. More specifically, the present invention relates to an ink composition having excellent clogging resistance, capable of stable ejection even when continuous printing is performed, and further having excellent print quality, water resistance, abrasion resistance and quick drying property. .

[0002]

2. Description of the Related Art Ink jet recording is a method in which ink droplets are formed using a mechanical or thermal action, and the ink droplets are ejected and fly to form an image on a recording material such as paper. Since this method does not include processes such as development and fixing as in the recording method of electrophotography and the like, it is possible to easily reduce the size of the apparatus and to record an image at high speed and with low noise. Usually, as the ink used in the ink jet recording method, an aqueous ink occupies the mainstream in terms of odor, safety, etc., and is composed of a solution in which various dyes or pigments are mixed with water and a water-soluble organic solvent as a dye. Ink is used.

The characteristics required for ink-jet recording inks include high print quality, quick drying, water resistance, abrasion resistance, storage stability, ejection stability, and the ability not to damage members such as a head. Intensive studies have been made on the composition and physical properties of inks that satisfy these requirements. However, since these characteristics are often in a mutually contradictory relationship, it is considerably difficult to satisfy the respective characteristics simultaneously with good balance. For example, if a penetrating agent that promotes the penetration of the ink into the recording medium is added to improve the drying property, the ink becomes liable to bleed, which adversely affects the print quality and the optical density. In addition, it has been considered to add a small amount of resin to the ink for the purpose of improving the abrasion resistance of the printed matter,
If the resin is water-soluble, the water resistance of the printed matter will decrease,
When the resin is water-dispersible, there is a problem that nozzles are likely to be clogged because water and highly volatile components evaporate from the ink ejection port, increasing the resin concentration and increasing the viscosity, and further forming a film. .

Japanese Patent Application Laid-Open No. 8-253716 discloses that acrylic acid
The water resistance of the ink is improved by using a terpolymer of styrene-α-methylstyrene. However, this method is inadequate in terms of drying time, and there is a possibility that the recording medium and the printed matter will be stained when continuous solid printing is performed. On the other hand, as a method of shortening the drying time, for example, in JP-A-8-209051,
Inks containing alcohol mixtures having a boiling point below ℃ have been reported. In this method, although the drying time of the printed matter is shortened, clogging resistance is insufficient because a low-boiling alcohol is used. As described above, in the case of the ink jet recording ink which has been conventionally reported, all the properties required for ink jet recording have not yet been satisfied.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has excellent clogging resistance and enables stable ejection even when continuous printing is performed.
Another object of the present invention is to provide an ink composition having excellent print quality, water resistance, abrasion resistance and quick drying property.

[0006]

Thus, according to the present invention, a water-soluble organic solvent, a pigment and a water-soluble resin comprising tert-butyl alcohol, neopentyl alcohol, N-methyl-2-pyrrolidone, diethylene glycol and polyethylene glycol are provided. At least, the balance being water, and the water-soluble organic solvent being 3 parts by weight based on the total weight of the ink composition.
-40% by weight, 0.1-20% by weight of pigment and 0.1
To 5% by weight of the ink composition for inkjet recording.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the ink composition of the present invention, a water-soluble organic solvent comprising tert-butyl alcohol, neopentyl alcohol, N-methyl-2-pyrrolidone, diethylene glycol and polyethylene glycol is used.

[0008] In addition to the above, water-soluble organic solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, se
Alkyl alcohols having 1 to 4 carbon atoms such as c-butyl alcohol; amides such as dimethylformamide and dimethylacetamide; ketones or ketone alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polypropylene glycol and the like Polyalkylene glycols having 2 to 6 alkylene groups such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol and hexylene glycol;
Alkylene glycols containing two carbon atoms; lower alkyl ethers of polyhydric alcohols such as glycerin, ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, and triethylene glycol monomethyl (or ethyl) ether;
2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, or the like may be used.

These water-soluble organic solvents are used in an amount of 3 to 40% by weight, preferably 4% by weight based on the total weight of the ink composition, for the purpose of preventing clogging at the nozzle tip and preventing the quality of printed matter from being degraded. It is used in the range of ~ 35% by weight.

[0010] In particular, in order to improve the clogging resistance, stabilize the ejection even during continuous printing, and obtain excellent quick drying without deteriorating the quality of the printed matter, the total weight of the ink composition is required. 0.5-5% by weight, preferably 1-5% by weight
Tert-butyl alcohol, 0.05-0.5 wt%, preferably 0.1-0.5 wt% neopentyl alcohol, 1-15 wt%, preferably 1-10 wt% N-methyl-2-pyrrolidone, each 1-10 It is preferred to use weight percent of diethylene glycol and polyethylene glycol. Above all,
Since polyethylene glycol greatly improves the ejection stability of the ink composition, the molecular weight is preferably in the range of 200 to 600.

As the pigment, known pigments can be used and are not particularly limited. However, for example, the pigments described below are preferably used. Examples of the carbon black used in the black ink include carbon blacks conventionally used in ordinary ink jet ink compositions, specifically, furnace black, lamp black, acetylene black, channel black, and the like. Pigments used in cyan ink compositions include CI Pigm
entBlue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 1
6, 17: 1, 56, 60, 63; pigments used in the magenta ink composition include CI Pigment Red 1, 2, 3, 5, 7, 1
7, 22, 23, 31, 38, 48: 2 (Ba), 48: 2 (Ca), 48: 3 (Sr), 4
8: 4 (Mn), 49: 1, 52: 2, 53: 1, 57: 1, 60: 1, 63: 1, 63:
2, 64: 1, 81, 83, 88, 101, 104, 105, 106, 108, 11
2, 114, 122, 123, 146, 149, 166, 168, 170, 172, 17
7, 178, 179, 185, 190, 193, 209, 219; pigments used in the yellow ink composition include CI Pigment Yell
ow1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42, 53, 5
5, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 10
9, 110, 117, 120, 128, 138, 153, 180 and the like.

The pigment is, for example, aniline black
Black organic pigments such as (CIPigment Black 1),
Orange 1, 2, 5, 7, 13, 14, 15, 16, 34, 36, 38;
I. Pigment Violet 1, 2, 19, 32; CI Pigment Green
1, 4, 36; CI Pigment Brown 3, 5, 25, 26, or the like may be used, or one newly manufactured for the present invention may be used.

The content of the pigment used in the ink of the present invention is determined in order to satisfy the color tone, density, or preferable ink properties required for a printed matter, and varies depending on the specific gravity and bulk density of the pigment. . However, from the viewpoint of securing print density and ejection stability,
The pigment is preferably used in the range of 0.1 to 20% by weight, particularly 1 to 15% by weight based on the total weight of the ink composition.

The pigment may be subjected to a surface treatment by a known means in order to improve wettability or impart self-dispersibility. For example, carbon black having a surface active group oxidized can be dispersed in ink without a dispersant, and can be suitably used in place of the above pigment. As such carbon black, for example, carbon black having a sulfonic acid group bonded to the surface (for example, trade name: CABOJET 200 (CAB-O-JET200), manufactured by Cabot (CABOT)), or a carboxyl group bonded to the surface Carbon black (for example, trade name: CABOJET 300, manufactured by Cabot Corp.).

However, even such a self-dispersible pigment does not prevent the use of a water-soluble resin described later. The water-soluble resin is used as a pigment dispersant to uniformly disperse the pigment in the ink. The water-soluble resin has a weight-average molecular weight of 1,000 to maintain the binder function of the resin and obtain stable ink ejection and robustness of printed matter.
It is preferably in the range of 0-15,000, especially 3,000-15,000.

Examples of such a resin include styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid, acrylic acid derivatives, maleic acid, and the like. Maleic acid derivative, itaconic acid, itaconic acid derivative, fumaric acid, fumaric acid derivative, vinyl acetate, vinylpyrrolidone, at least two or more monomers selected from acrylamide and derivatives thereof (however,
Among them, a block copolymer composed of at least one of which is a hydrophilic monomer), a random copolymer, a graft copolymer, a salt thereof, and the like can be given. Further, natural resins such as rosin, shellac and starch can also be preferably used.

Of these, styrene-acrylic acid copolymers are preferred because they significantly improve the water resistance and abrasion resistance of the ink composition. Styrene-acrylic acid copolymers include, for example, Joncryl J-67, 678, 586, 680, 68
2, 683 (trade name, manufactured by Johnson Polymer Co., Ltd.) and the like. These resins are alkali-soluble resins soluble in an aqueous solution in which a base is dissolved, and are preferably contained in the range of 0.1 to 5% by weight based on the total weight of the ink composition.

In order to obtain desired physical properties as required, a surfactant other than the above, a defoaming agent,
Fungicides, preservatives, rust inhibitors and the like can be added.
Further, the ink may contain urea, thiourea, ethylene urea or derivatives thereof as a nozzle drying inhibitor.

As the surfactant, any of anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants can be used. For example, as anionic surfactants, higher fatty acid salts, alkyl sulfates, alkyl ether sulfates, alkyl ester sulfates, alkyl aryl ether sulfates, alkyl sulfonates, sulfosuccinates, alkyl allyls and alkyl naphthalene sulfonates, alkyls Phosphates, polyoxyethylene alkyl ether phosphates, alkyl aryl ether phosphates and the like.

Examples of the cationic surfactant include alkylamine salts, dialkylamine salts, tetraalkylammonium salts, benzalkonium salts, alkylpyridinium salts, and imidazolinium salts.
Nonionic surfactants such as dimethylalkyl lauryl betaine, alkyl glycine, alkyl di (aminoethyl) glycine, imidazolinium betaine, etc., include polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene polyoxypropylene glycol, Glycerin ester, sorbitan ester, sucrose ester, polyoxyethylene ether of glycerin ester, polyoxyethylene ether of sorbitan ester, polyoxyethylene ether of sorbitol ester, fatty acid alkanolamide, polyoxyethylene fatty acid amide, amine oxide, polyoxyethylene Alkylamines and the like can be used.

Specific examples of the antifoaming agent include ethyl alcohol, isopropyl alcohol and the like. Specific examples of fungicides, preservatives, and rust inhibitors include benzoic acid, dichlorophen, hexachlorophen, sorbic acid, p-hydroxybenzoate, ethylenediaminetetraacetic acid (EDT
A), sodium dehydroacetate, 1,2-benzothiazoline-3
-One and 3,4-isothiazolin-3-one.

The method for preparing the ink composition of the present invention is not particularly limited. For example, a pigment dispersion obtained by adding a pigment and a water-soluble resin in an aqueous medium in advance is added to and mixed with a water-soluble organic solvent. Can be manufactured.
In this case, the pigment dispersion is first premixed to make the water-soluble resin, alkali neutralizer (pH adjuster) and dissolution aid uniform in the aqueous medium, and then to add the pigment and shake the components. Further, the dispersion can be obtained by performing dispersion using a commonly used dispersing machine, for example, a ball mill, a roll mill, a sand mill, or the like, and centrifuging as necessary.

The pigment dispersion is prepared by reducing the size of the pulverizing medium of the dispersing machine, increasing the filling rate of the pulverizing medium, increasing the processing time, or classifying the pulverized medium by a filter or centrifugal separation after pulverization, or a combination thereof. By combination, a dispersion having a particle size distribution in a desired range may be obtained. It is preferable that the water-soluble organic solvent to which the pigment dispersion is added is sufficiently filtered after dilution by centrifugal filtration using a centrifuge or a membrane filter having a pore size of 5 μm or less.

The physical properties of the ink composition thus prepared can be appropriately adjusted. However, in order to stably eject the ink composition from the ejection head, for example, the viscosity at 25 ° C. is 25 mPa · s or less. And more preferably 10 mPa · s or less. Also,
The surface tension preferably ranges from 20 to 50 mN / m at 25 ° C.

As a recording apparatus suitable for performing recording using the ink composition of the present invention, an on-demand type or a continuous type ink jet apparatus which performs printing on a recording material by ejecting ink is exemplified. As a method of ink ejection, thermal energy corresponding to a recording signal is applied to ink in the recording head chamber, and a droplet is generated and ejected by the energy, or a thermal jet method in which ink in the recording head chamber corresponds to the recording signal. Any of a piezoelectric element type in which a piezoelectric element pressurizes and ejects the liquid may be used.

The recording medium to which the ink composition of the present invention is adhered is not particularly limited, and examples thereof include papers exclusively for inkjet printing, PPC paper, and plain paper known in the art.

[0027]

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example 1: (Preparation of carbon black dispersion) Styrene-acrylic acid copolymer resin 6% by weight (weight average molecular weight Mw = 12,500) (manufactured by Johnson Polymer) Dimethylaminoethanol 6% by weight Isopropyl alcohol 0.4% by weight Pure water 77.6% by weight The above components were completely dissolved under heating at 70 ° C.

Next, 10% by weight of carbon black (MA-100; manufactured by Mitsubishi Chemical Corporation) was added to the above solution, and premixing was performed, followed by dispersion with a ball mill (manufactured by Fritsch).
(Zirconium beads filling rate = 50%; Media diameter = 0.5m
m) and centrifugation (12000 rpm) to remove coarse particles, thereby obtaining a carbon black dispersion.

(Preparation of Ink Composition) An ink composition was prepared by mixing and stirring according to the following formulation, and removing dust and coarse particles by filtering through a 1.2 μm filter. The above carbon black dispersion 50% by weight tert-butyl alcohol 2% by weight neopentyl alcohol 0.3% by weight N-methyl-2-pyrrolidone 5% by weight Diethylene glycol 5% by weight Polyethylene glycol Mw400 5% by weight Pure water 32.7% by weight

Example 2: (Preparation of resin liquid) Styrene-acrylic acid copolymer resin 6% by weight (weight average molecular weight Mw = 12,500) dimethylaminoethanol 6% by weight isopropyl alcohol 0.4% by weight Pure water 77.6% by weight Was completely dissolved under heating at 70 ° C.

(Preparation of Ink Composition) An ink composition was prepared by mixing and stirring according to the following formulation, and removing dust and coarse particles by filtering through a 1.2 μm filter. 50% by weight of the above resin solution 5% by weight of Cabojet 300 (manufactured by Cabot) 2% by weight of tert-butyl alcohol 0.3% by weight of neopentyl alcohol 5% by weight of N-methyl-2-pyrrolidone 5% by weight of diethylene glycol 5% by weight of polyethylene glycol Mw400 Water 27.7% by weight

Example 3 Using the resin liquid of Example 2, an ink composition was prepared in the same manner as described below. Resin liquid of Example 2 33.3% by weight Cabojet 300 (manufactured by Cabot) 5% by weight tert-butyl alcohol 3% by weight neopentyl alcohol 0.1% by weight N-methyl-2-pyrrolidone 8% by weight Diethylene glycol 3% by weight Polyethylene glycol Mw400 5 42.6% by weight of pure water

Example 4: The carbon black of Example 1 was used
Pigment Red 122 (Dainichi Seika)
An ent Red 122 dispersion was prepared, and an ink composition was similarly prepared with the following formulation. Pigment Red 122 dispersion 50% by weight tert-butyl alcohol 2% by weight neopentyl alcohol 0.3% by weight N-methyl-2-pyrrolidone 5% by weight Diethylene glycol 5% by weight Polyethylene glycol Mw400 5% by weight Pure water 32.7% by weight

Comparative Example 1 An ink composition was prepared in the same manner as in Example 3 except that polyethylene glycol Mw400 in Example 3 was replaced with polyethylene glycol Mw1000. Comparative Example 2: The styrene-acrylic acid copolymer resin (weight average molecular weight Mw = 12,500) of Example 4 was replaced with a styrene-acrylic acid copolymer resin (weight average molecular weight Mw = 17,000). Ink composition was prepared in the same manner as in No. 4.

Comparative Example 3 A styrene-acrylic acid copolymer resin (weight average molecular weight Mw = 12,500) of Example 4 was replaced with a styrene-maleic acid copolymer resin (weight average molecular weight Mw = 13,000).
Then, an ink composition was prepared in the same manner as in Example 4. Comparative Example 4: An ink composition was prepared in the same manner as in Example 1 except that the polyethylene glycol Mw400 of Example 1 was not added.

Comparative Example 5 An ink composition was prepared in the same manner as in Example 4 except that the neopentyl alcohol of Example 4 was not added. Comparative Example 6: diethylene glycol of Example 2, N-methyl
2-Pyrrolidone and styrene-acrylic acid copolymer resin
(Weight average molecular weight Mw = 12,500) was not added, and the rest was prepared in the same manner as in Example 2.

(Experiment) Experiment 1: Continuous printing test The ink composition was manufactured using an inkjet printer A manufactured by Sharp.
We examined the number of printable sheets when printing was performed continuously at a print density of 15% using a J2000 modified machine. The number of printable sheets until the ink tank is filled with the ink composition and becomes empty is about 200 sheets. In the experiment, when the ink composition became empty, the ink composition was refilled, and this operation was repeated until printing could not be performed, and the number of sheets that could be printed up to that time was regarded as the number of printable sheets. PPC paper (SF-4AM3 made by Sharp) for recording material
Was used, and when the number of printable sheets exceeded 400, it was evaluated as ○, and when it was less than 400, it was evaluated as ×.

Experiment 2: Clogging test After packing the ink composition in a cartridge and printing 10 sheets on a recording material using PPC paper (SF-4AM3 manufactured by Sharp),
The ink cartridge was removed from the printer and left at room temperature for 7 days without capping. After the standing, the ink cartridge was attached to the printer again, and the cleaning operation was performed two or three times.

Experiment 3: Drying test The ink composition was packed in a cartridge, printed on a commercially available PPC paper (manufactured by Oji Paper Co., Ltd.), the printed portion was rubbed with a finger, and the time (sec) until the finger or the paper became clean was removed. ) Was measured. The case where the drying time was within 60 seconds was evaluated as ○, the case where the drying time was 61 to 90 seconds was evaluated as Δ, and the case where the drying time was 91 seconds or longer was evaluated as ×.

Experiment 4: Water resistance test The ink composition was packed in a cartridge, printed on a commercially available PPC paper (manufactured by Oji Paper Co., Ltd.), left for 6 hours, immersed in tap water for 5 minutes, and tested for optical density before and after the test. Measure the value and determine the residual rate (%)
Was calculated. The case where the residual ratio was 95% or more was rated as ○, the case where it was 90 to 94% was rated as Δ, and the case where it was 89% or less was rated as ×.

Experiment 5: Fixing property test The ink composition was packed in a cartridge, solid printing was performed on a commercially available PPC paper (manufactured by Oji Paper Co., Ltd.), and the printed portion was rubbed three times with a wet cotton swab. The change was visually evaluated.
The case where there was no rubbing was evaluated as ○, and the case where there was rubbing was evaluated as x.

Experiment 6: Print Quality The ink composition was packed in a cartridge, printed on a commercially available PPC paper (manufactured by Oji Paper Co., Ltd.), and evaluated visually. The case of good was marked with ○, and the case of bad was marked with x. Table 1 shows the composition weight% of the ink composition and the results of Experiments 1 to 6.

[Table 1]

As described above, an ink composition which is excellent in clogging resistance, capable of stable ejection even in continuous printing, and excellent in the quality of printed matter, water resistance, abrasion resistance and quick drying is used. It can be obtained in the invention.

[0044]

According to the present invention, at least a water-soluble organic solvent comprising tert-butyl alcohol, neopentyl alcohol, N-methyl-2-pyrrolidone, diethylene glycol and polyethylene glycol, a pigment and a water-soluble resin are contained, and the balance Is water, and the water-soluble organic solvent is 3 to 40% by weight, the pigment is 0.1 to 20% by weight, and the water-soluble resin is 0.1 to 5% by weight based on the total weight of the ink composition. A recording ink composition is provided.
In this composition, the water-soluble organic solvent improves the clogging resistance in particular, stabilizes ejection even when continuous printing is performed,
Further, in order to obtain excellent quick-drying without impairing the quality of the printed matter, 0.5 to 5% by weight of te based on the total weight of the ink composition is used.
rt-butyl alcohol, 0.05-0.5% by weight neopentyl alcohol, 1-15% by weight N-methyl-2-pyrrolidone, each
It preferably comprises from 1 to 10% by weight of diethylene glycol and polyethylene glycol. Further, when the molecular weight of polyethylene glycol is in the range of 200 to 600, the ejection stability of the ink composition can be greatly improved. Furthermore, the water-soluble resin has a weight average molecular weight of 1,00
By being in the range of 0 to 15,000, preferably 3,000 to 15,000, the binder function of the resin can be maintained, and stable ink ejection and the robustness of printed matter can be obtained. By use, the water resistance and rub resistance of the ink composition can be significantly improved.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kiyoto Motoyama 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroaki Nakaya 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Masaru Nakamura 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Prefecture Inside Sharp Corporation (72) Hiromi Nakatsu 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Corporation F term (reference) 2C056 FC01 2H086 BA01 BA53 BA55 BA59 BA60 BA62 4J039 AD03 AD09 AE07 BC07 BC11 BC49 BE01 BE12 CA03 CA06 EA10 EA36 EA38 EA41 EA42 EA46 GA24

Claims (5)

[Claims] 1. A water-soluble organic solvent comprising (a) tert-butyl alcohol, neopentyl alcohol, N-methyl-2-pyrrolidone, diethylene glycol and polyethylene glycol, (b) a pigment, and (c) a water-soluble resin. Water-soluble organic solvent (a) based on the total weight of the ink composition;
0.1 to 20% by weight of (b) and 0.1 to 5% by weight of water-soluble resin (c)
An ink composition for ink-jet recording, characterized in that: 2. A water-soluble organic solvent (a) comprising 0.5 to 5% by weight of tert-butyl alcohol based on the total weight of the ink composition;
2. The ink composition according to claim 1, comprising 0.05 to 0.5% by weight of neopentyl alcohol, 1 to 15% by weight of N-methyl-2-pyrrolidone, 1 to 10% by weight of diethylene glycol and polyethylene glycol, respectively. 3. The ink composition according to claim 1, wherein the weight average molecular weight of the polyethylene glycol is from 200 to 600. 4. The water-soluble resin (c) has a weight average molecular weight of 1,000.
The ink composition according to any one of claims 1 to 3, wherein the amount is from 15,000 to 15,000. 5. The ink composition according to claim 1, wherein the water-soluble resin (c) is a copolymer of styrene-acrylic acid or a derivative thereof.