JP2002256185A - Water-based ink composition for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based ink composition which can give a printed matter very excellent in water resistance and exhibiting high delivering stability and storage stability. SOLUTION: A specified image sample is made in duplicate. Two image samples are left under respective temperature conditions different from each other for a specified time and are subsequently subjected to a specified immersion operation in water. Then, optical density of each image sample is measured. The difference in optical density between the two image samples is set to a specified value or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ink used in an ink jet recording method and apparatus.

[0002]

2. Description of the Related Art Inkjet printers (IJ printers) do not require processes such as development and fixing.
Since colorization is very easy and printing on plain paper is possible, it has been dramatically spread. In particular, recently, high-definition color printers and the like corresponding to photographic images are commercially available, and this type of printer is becoming the mainstream of inkjet printers. Therefore, recent inkjet printers are required to handle photographic images.
Printed materials produced by IJ printers are required to have image quality and storage stability as well as stability equivalent to silver halide photographs. For this reason, in order to improve the storage stability of printed matter, that is, the weather resistance performance, it is desired that the IJ ink used in the IJ printer also has high water resistance.

[0003] In general, IJ inks are roughly classified into dye inks using an aqueous dye as a colorant, and pigment inks in which a pigment is dispersed in water as a colorant.

[0004] Japanese Patent Application Laid-Open No. 56-14763 discloses I
Pigment inks for J printers have been proposed. This ink has excellent water resistance of a printed image, but has poor dispersion stability as an IJ ink, and has a problem of causing clogging or the like at the time of ink ejection.

As pigment inks having improved dispersion stability and ejection stability, pigment inks to which a special water-soluble resin has been added are disclosed in JP-A-6-100810 and JP-A-6-12.
No. 2846 has been proposed. However, these pigment inks also did not satisfy the ejection characteristics required for photographic image printers that eject minute droplets.

As described above, pigment inks are difficult to use as inks for photographic image printers. Therefore, dye inks are mainly used in current color printers. However, while a clear image can be obtained with the dye ink, a problem is that the water resistance is inferior as a problem.

Therefore, as a highly water-resistant dye ink, an aqueous ink to which a specific resin is added is disclosed in JP-A-11-323.
No. 230 has been proposed. However, this ink still did not satisfy the required water resistance performance.

On the other hand, as a method for improvement from the side of a recording medium, a method using a recording sheet formed by a special processing method as disclosed in Japanese Patent Application Laid-Open No. 1-259879 has been proposed. However, even with this method, the required water resistance is not yet satisfied, and it is not practically excellent because it is more expensive than plain paper.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water-based ink having extremely excellent water resistance and capable of obtaining a printed matter having high ejection stability and storage stability. Another object of the present invention is to provide an ink jet recording method and an ink jet recording apparatus using the same.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have made an aqueous ink composition for ink jet recording containing a colorant, an organic solvent and a surfactant, wherein the amount of one droplet is 20. Under a condition of picoliter and a resolution of 720 dpi, first and second images are formed using an ink jet recording method so that droplets are arranged in all pixels, and the first image is left at room temperature for 3 hours. Then, the optical density of the image when immersed in pure water at 25 ° C. and dried at room temperature for 3 hours is defined as a first optical density (OD1).
When the optical density of the image when left at α ° C. selected from 80 ° C. for 3 hours, immersed in pure water at 25 ° C., and dried at room temperature for 3 hours is defined as a second optical density (OD2), The aqueous ink composition for inkjet recording in which the first optical density (OD1) and the second optical density (OD2) satisfy the relationship of OD2−OD1 ≧ 0.05 gives a printed matter having excellent water resistance. The present inventors have found that the ejection stability and the storage stability are excellent in spite of little bleeding, and have completed the present invention.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous ink composition of the present invention contains a colorant, an organic solvent, and a surfactant, and these are at least dispersed or dissolved in an aqueous medium. Then, the aqueous ink composition of the present invention prepares two specific image samples, is left for a predetermined time under different temperature conditions, and then performs a specific water immersion operation on each image sample. The difference between the optical densities of the images of the respective image samples is characterized by being equal to or more than a specific value, thereby realizing high water resistance, ejection stability and storage stability. One of the two temperature conditions can be appropriately selected from the range of 30 ° C. or more and 80 ° C. or less.
° C ”. As α ° C., preferably 50 ° C. or more and 80 ° C. or less, more preferably 50 ° C. or 80 ° C. is selected. The other of the two temperature conditions is room temperature. Here, room temperature means a temperature range of 20 ° C. or more and less than 30 ° C., and preferably 25 ° C.

Hereinafter, a method for preparing an image sample, a method for dipping in water, and a method for measuring optical density, which are essential for specifying the ink composition of the present invention, will be described in detail.

The image sample has an ink droplet amount of 2
A piezo-type inkjet printer adjusted to be 0 picoliter is manufactured by discharging aqueous ink onto plain paper under the condition of a resolution of 720 dpi so that droplets are arranged on all pixels. The plain paper is not particularly limited as long as it is a commercially available plain paper.
x L is used.

In the operation of immersing the image sample in water, a glass water tank (capacity: 10 L) is filled with pure water at 25 ° C., and the entire image surface of the image sample is immersed in water.
This is done by leaving the image sample out of the water tank and drying at room temperature for 3 hours.

The optical density measurement was performed using RD918 manufactured by Macbeth.
This is performed using an optical densitometer. It is preferable that a filter for the ink be used for the color ink, a cyan filter be used for the cyan ink, a magenta filter be used for the magenta ink, and a yellow filter be used for the yellow ink.

In the present invention, the coloring material is a dye or a pigment and is not particularly limited as long as it contributes to coloring in the ink, but it is preferable to use a water-soluble dye.
Examples of the water-soluble dye include acid dyes, basic dyes, direct dyes, food dyes, and the like. Specific examples include direct black 19, direct black 32, direct black 38, direct black 51, direct black 62, and direct black. 71, Direct Black 105, Direct Black 108, Direct Black 112, Direct Black 154, Direct Black 168, Direct Black 171, Acid Black 24, Acid Black 31, Acid Black 52, Acid Black 94, Food Black 1, Food Black 2, Direct Yellow 23, Direct Yellow 50, Direct Yellow 86, Direct Yellow 100, Direct Yellow 132, Direct Yellow 142, Die ECTS Yellow 157, Acid Yellow 23, Acid Yellow 42, Direct Red 83, Direct Red 227, Acid Red 35,
Acid Red 40, Acid Red 52, Acid Red 87, Acid Red 186, Acid Red 25
4, Acid Red 289, Reactive Red 24,
Reactive Red 120, Reactive Red 18
0, direct blue 76, direct blue 86, direct blue 108, direct blue 199, direct blue 236, acid blue 9, acid blue 78, acid blue 82, acid blue 86, acid blue 234, and the like. Without limitation, any water-soluble dye can be used. The amount of the dye is 1 to 10 with respect to the total weight of the ink composition.
% By weight is preferred. When the dye is added in an amount of 10% by weight or more, the stability as an ink is deteriorated, clogging is likely to occur in a head discharge portion of an ink jet printer or the like, and the viscosity is greatly increased. On the other hand, when the amount of the dye is less than 1% by weight, there is a problem that a good image cannot be obtained because the dye concentration is low.

In the aqueous ink of the present invention, it is preferable to use water as an aqueous medium for dissolving or dispersing a colorant, particularly a dye. As the water, ion-exchanged water is preferable from the viewpoint of dye stability, but commercially available distilled water may be used.

The organic solvent used in the aqueous ink of the present invention is not particularly limited. Examples thereof include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol MW200, polyethylene glycol MW300, and polyethylene glycol. MW600,
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methyl carbitol, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, diethyl carbitol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, Examples include triethylene glycol monobutyl ether, glycerin, triethanolamine, formamide, dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, 1,3-dimethylimidazolidine and the like. Among these organic solvents, at least one organic solvent selected from the group consisting of diethylene glycol, propylene glycol, polyethylene glycol, glycerin, triethylene glycol monobutyl ether and diethylene glycol monobutyl ether has ink storage stability, recording paper It is suitably used from the viewpoint of permeability to water.

These organic solvents are used as penetrants and dye dissolution aids, and their amounts are preferably 50% by weight or less based on the total weight of the ink composition. If the compounding amount of the organic solvent exceeds 50% by weight, the drying property on the recording paper is deteriorated, and a good printed image may not be obtained.

The surfactant contained in the ink composition of the present invention is not particularly limited, but it is preferable to use a non-ionic surfactant. Examples of the nonionic surfactant include an acetylene glycol-based compound and a propylene oxide-ethylene oxide copolymer, but are not particularly limited thereto. The amount of the surfactant is 0.1% based on the total weight of the ink composition.
It is preferably from 01% to 10% by weight. 0.01% by weight
If the compounding amount is less than the above, the amount is too small, so that a sufficient surface tension adjusting effect cannot be obtained. On the other hand, when the content is 10% by weight or more, the viscosity of the ink is greatly increased because the amount is too large.

The ink composition of the present invention contains a pH adjuster,
Conventionally known additives such as an antifungal agent and a chelating agent can be mixed. Examples of the pH adjuster include potassium carbonate, sodium carbonate, and triethanolamine. Examples of the fungicide include sodium benzoate. Examples of the chelating agent include sodium diethylenetriaminepentaacetate.

The ink composition of the present invention has a surface tension of 25.
It is preferably 20 to 50 dyne / cm at ° C.
The surface tension in the present invention is a static surface tension when the liquid surface is at rest, and can be measured by a Wilhelmy plate hanging method or the like. Static surface tension is 5
More than 0 dyne / cm or 20 dyne / cm
When the aqueous ink is less than the above, the permeability and the drying property are deteriorated at the time of forming an image, and a good printed image may not be obtained.

The viscosity of the ink composition of the present invention is preferably adjusted to a range of 1 to 5 cps at 25 ° C.
In the case of an aqueous ink having a viscosity of more than 5 cps or less than 1 cps, the ink ejection stability of the head is deteriorated, and a good printed image may not be obtained.

The pH of the ink composition of the present invention is 2
Preferably, the temperature is adjusted to 6.5 to 11.5 at 5 ° C. By adjusting the pH of the ink to 6.5 to 11.5, the long-term storage property of the ink is improved, changes in various physical properties such as surface tension and viscosity are reduced, and
Stable ink ejection becomes possible.

When a water-soluble dye is used in the ink composition of the present invention, a printed matter having particularly high ejection stability and excellent in sharpness can be obtained.

Although the use of the ink composition of the present invention is not particularly limited, it can be used in an ink jet recording method and apparatus in which ink droplets are ejected from a fine orifice by the action of a piezo element to perform recording. preferable.

The ink composition of the present invention is used by being incorporated in an ink container. The ink container has a storage chamber for storing the ink composition of the present invention, and at least a portion of the storage chamber that contacts the ink may be made of a material that is inert to the ink composition of the present invention. preferable. The material inert to the ink composition of the present invention is a material that is at least insoluble in the ink composition of the present invention and a material that does not adversely affect the ink composition of the present invention during storage, such as deterioration. For example, a resin such as polypropylene, a metal such as aluminum, or a ceramic.

The ink jet recording apparatus of the present invention has an ink discharge port for discharging the ink composition of the present invention, and can record an image or the like on a recording medium such as paper using the ink of the present invention. . As described above, the ink composition of the present invention is used for an ink jet recording apparatus that performs recording by discharging ink droplets, but its use is not particularly limited.

Since such an ink jet recording apparatus and ink jet recording method use the aqueous ink composition of the present invention, they are excellent in ejection stability and storage stability, and particularly have extremely excellent water resistance. You can get printed matter.

[0030]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples, but it goes without saying that the present invention is not limited to these Examples.

(Preparation of Image Sample) Using a piezo-type ink jet printer adjusted so that the amount of one ink droplet becomes 20 pl (picoliter), a resolution of 72 is used.
Under the condition of 0 dpi, the aqueous ink was applied to two plain papers in a size of 2 cm × 2 cm so that the droplets were arranged on all the pixel grids.
To obtain two image samples. Xerox L paper was used as plain paper.

(Water immersion operation) One of the two image samples was left at room temperature for 3 hours, and the other was left at a temperature (α ° C.) selected from 30 to 80 ° C. for 3 hours. Next, both of these image samples were immersed in pure water. In this example, two temperatures of 50 ° C. and 80 ° C. were adopted as α ° C. At the time of immersion, a glass water tank (capacity 10
L) was filled with pure water at 25 ° C., the image portion of the image sample was immersed in water over the entire surface, and left at 25 ° C. for 5 minutes.
The image sample pulled out of the water tank was dried at room temperature for 3 hours. (Static surface tension) It was measured using a Wilhelmy type surface tensiometer (automatic surface tensiometer CBVP-A3, manufactured by Kyowa Interface Chemical Co., Ltd.). The measurement temperature was 25 ° C.

(Viscosity) The viscosity was measured by an automatic viscosity meter DVM-EII (manufactured by Tokimec). The measurement temperature was 25 ° C.

(PH) Personal pH meter PH81
(Manufactured by Yokogawa Electric Corporation). The measurement temperature was 25 ° C.

(Evaluation of Water Resistance 1) The optical density (OD value) of the image sample was measured. The optical density of each image sample was measured before and after the above-mentioned water immersion operation, and the variation ΔD of the OD value before and after the water immersion was calculated as a judgment index of the water resistance performance. The optical density was measured using an RD918 type optical densitometer manufactured by Macbeth.

(Evaluation 2 of Water Resistance) The color values (L ^* , a ^* , b ^* ) of the image (solid) portion of the image sample were measured using the L ^* a ^* b ^* color system (CIELAB color system). The color was measured. For each image sample, the color values (L1 ^* ,
a1 ^* , b1 ^* ) and the color values (L2 *, a2) after the water immersion operation.
*, B2 *) were measured using the L ^* a ^* b ^* color system. As a judgment index of water resistance performance, a water resistance deterioration change rate ΔE was calculated by the following equation (1).

Equation (1) ΔE = ｛(L1 ^* −L2 ^* ) ² + (a1 ^* −a2 ^* ) ² + (b
1 ^* -b2 ^* ) ² ｝ ^1/2 color value was measured using a 938 Spectro-Densitometer (manufactured by X-Rite).

(Evaluation of Ejection Stability) A printing test was performed on 100 sheets using a piezo-type inkjet printer with a resolution of 720 dpi adjusted so that the amount of one ink droplet was 10 pl (picoliter). Commercially available recycled paper (A4 size) was used as the printing paper.

The sharpness of the image was confirmed for 100 print samples, and the ejection stability was evaluated according to the following evaluation criteria. ：: All are good printed images. Δ: Most of the images were good, but some abnormal images were observed. ×: Many abnormal printed images were observed.

(Evaluation of Storage Stability) The aqueous ink was stored in a polyethylene container at 60 ° C. for one month, examined for changes in surface tension, viscosity and pH, and for the presence or absence of precipitates. The sex was evaluated. ：: There is almost no change in physical properties, and no precipitate is observed. Δ: Physical properties were slightly changed, but no precipitate was observed. ×: Physical properties are significantly changed, and precipitates are confirmed.

Example 1 Ink Composition 1 Reactive Red 24 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 2 parts Ion-exchanged water Remainder In the ink composition of Example 1, , Surface tension γ = 30.4 dyn
e / cm, viscosity η = 3.3 cps, pH = 9.0.

Example 2 Ink Composition 2 Reactive Red 24 1 part Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 2 parts Ion-exchanged water Remainder In the ink composition of Example 2, , Surface tension γ = 30.8 dyn
e / cm, viscosity η = 3.0 cps, pH = 8.4.

Example 3 Ink Composition 3 Reactive Red 24 5 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 2 parts Ion-exchanged water Remainder In the ink composition of Example 3, , Surface tension γ = 30.2 dyn
e / cm, viscosity η = 3.5 cps, pH = 9.3.

Example 4 Ink Composition 4 Reactive Red 24 2 parts Acid Red 52 1 part Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Deionized water Remainder Example 4 In the ink composition, the surface tension γ = 30.4 dyn
e / cm, viscosity η = 3.1 cps, pH = 8.5.

Example 5 Ink Composition 5 Reactive Red 24 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Water-soluble resin 5 parts Nonionic surfactant 1 part Triethanolamine 2 parts Deionized water Remainder Example 5 In the ink composition, the surface tension γ = 30.1 dyn
e / cm, viscosity η = 3.9 cps, pH = 9.1.

Example 6 Ink Composition 6 Acid Red 37 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 2 parts Ion-exchanged water Remainder In the ink composition of Example 5, , Surface tension γ = 30.9 dyn
e / cm, viscosity η = 3.0 cps, pH = 8.6.

Example 7 Ink Composition 7 Direct Red 225 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Water-soluble resin 5 parts Nonionic surfactant 1 part Triethanolamine 2 parts Deionized water Remainder Example 7 In the ink composition, the surface tension γ = 30.6 dyn
e / cm, viscosity η = 4.1 cps, pH = 9.1.

Example 8 Ink Composition 8 Reactive Blue 80 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Water-soluble resin 5 parts Nonionic surfactant 1 part Triethanolamine 1 part Deionized water Remaining Example 6 In the ink composition, the surface tension γ = 30.1 dyn
e / cm, viscosity η = 3.1 cps, pH = 8.3.

Example 9 Ink Composition 9 Reactive Yellow 15 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remainder The ink composition of Example 9 , Surface tension γ = 30.5 dyn
e / cm, viscosity η = 3.12 cps, pH = 9.1.

Example 10 Ink Composition 10 Reactive Yellow 55 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remainder The ink composition of Example 10 , Surface tension γ = 30.1 dy
ne / cm, viscosity η = 3.0 cps, pH = 9.5.

Example 11 Ink Composition 11 Reactive Yellow 55 2 parts Acid Yellow 142 1 part Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remaining Example 11 In the ink composition, the surface tension γ = 30.1 dy
ne / cm, viscosity η = 3.1 cps, pH = 9.2.

Example 12 Ink Composition 12 Reactive Yellow 55 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Water-soluble resin 5 parts Nonionic surfactant 1 part Triethanolamine 1 part Deionized water Remaining Example 12 In the ink composition, the surface tension γ = 30.4 dy
ne / cm, viscosity η = 4.1 cps, pH = 9.3.

Example 13 Ink Composition 13 Reactive Black 17 6 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remainder The ink composition of Example 13 , Surface tension γ = 30.1 dy
ne / cm, viscosity η = 3.5 cps, pH = 9.8.

Comparative Example 1 Ink Composition 14 Acid Red 52 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remainder The ink composition of Comparative Example 1 , Surface tension γ = 30.3 dyn
e / cm, viscosity η = 3.1 cps, pH = 9.1.

Comparative Example 2 Ink Composition 15 Acid Red 52 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Water-soluble resin 5 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remaining Comparative Example 2 In the ink composition, the surface tension γ = 30.5 dyn
e / cm, viscosity η = 3.0 cps, pH = 9.2.

[Comparative Example 3] Ink Composition 16 Reactive Red 97 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remainder The ink composition of Comparative Example 3 , Surface tension γ = 30.7 dyn
e / cm, viscosity η = 3.9 cps, pH = 9.1.

Comparative Example 4 Ink Composition 16 Direct Blue 90 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Triethanolamine 1 part Ion-exchanged water Remainder The ink composition of Comparative Example 4 , Surface tension γ = 30.3 dyn
e / cm, viscosity η = 3.1 cps, pH = 9.4.

[Comparative Example 5] Ink Composition 17 Direct Yellow 120 3 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Ion-exchanged water balance In the ink composition of Comparative Example 5, the surface tension γ = 30.2 dyn
e / cm, viscosity η = 3.0 cps, pH = 9.1.

Comparative Example 6 Ink Composition 17 Food Black 2 6 parts Polyethylene glycol # 200 15 parts Glycerin 10 parts Nonionic surfactant 1 part Ion-exchanged water balance The ink composition of Comparative Example 6 had a surface tension γ = 30.1dyn
e / cm, viscosity η = 3.4 cps, pH = 9.3.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Table 3]

[0063]

As described above, the aqueous ink composition for ink jet recording of the present invention has a droplet volume of 20 droplets.
The first and second liquid droplets are arranged on all the pixel grids under a resolution of 720 dpi in picoliters.
Is formed using an inkjet recording method, and the first image is formed.
Image was left at room temperature for 3 hours, immersed in pure water at 25 ° C,
The optical density of the image when dried at room temperature for 3 hours is defined as a first optical density (OD1), and the second image is defined as 30 to 80.
When the optical density of the image when left for 3 hours at α ° C selected from ° C, immersed in pure water at 25 ° C, and dried at room temperature for 3 hours is defined as a second optical density (OD2), The first optical density (OD1) and the second optical density (OD2) are OD
2-OD1 ≧ 0.05
It has high ejection stability and storage stability, and has very good water resistance. Therefore, a printed matter printed or formed with the aqueous ink composition can have improved weather resistance, which has been a problem in the past.

In the ink jet recording method and the recording apparatus of the present invention, recording is carried out by discharging an ink liquid from micropores in accordance with a recording signal, and the aqueous ink composition of the present invention is used as the ink. Therefore, it is possible to obtain a printed material having excellent ejection stability and storage stability, and having extremely excellent water resistance.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroyuki Ueki 5-7-1 Shiba, Minato-ku, Tokyo F-term in NEC Corporation 2C056 EA13 FC01 2H086 BA53 BA56 BA60 BA61 BA62 4J039 AE07 BC07 BC09 BC10 BC11 BC13 BC15 BE01 BE03 BE04 BE05 BE06 BE12 BE22 BE28 BE30 CA03 CA06 EA38 EA44 EA48 GA24

Claims (14)

[Claims] 1. A water-based ink composition for ink-jet recording comprising a colorant, an organic solvent and a surfactant, wherein the droplet volume is 20 picoliters and the resolution is 720d.
Under the conditions of pi, the first and second images are formed using the ink jet recording method so that the liquid droplets are arranged in all the pixels. The optical density of the image when immersed in pure water and dried at room temperature for 3 hours is defined as a first optical density (OD1), and the second image is left at α ° C selected from 30 to 80 ° C for 3 hours. Then, the image was immersed in pure water at 25 ° C. and dried at room temperature for 3 hours.
2. The aqueous ink composition for ink-jet recording as set forth in 2), wherein the first optical density (OD1) and the second optical density (OD2) satisfy a relationship of OD2−OD1 ≧ 0.05. 2. The ink composition according to claim 1, wherein the ink jet recording method includes a step of forming the ink composition into droplets using a piezoelectric vibrator. 3. The ink composition according to claim 1, wherein the coloring material is a water-soluble dye. 4. The ink composition according to claim 3, wherein the dye is contained in an amount of 1 to 10% by weight based on the total weight of the ink composition. 5. The method according to claim 1, wherein the organic solvent is ethylene glycol,
The method according to any one of claims 1 to 4, wherein the compound is one or more selected from the group consisting of diethylene glycol, propylene glycol, polyethylene glycol, glycerin, triethylene glycol monobutyl ether and diethylene glycol monobutyl ether. Ink composition. 6. The ink composition according to claim 1, wherein the organic solvent is contained in an amount of 1 to 50% by weight based on the total weight of the ink composition. 7. The ink composition according to claim 1, wherein the surfactant is a nonionic surfactant. 8. The ink composition according to claim 1, wherein the surfactant is contained in an amount of 0.01 to 10% by weight based on the total weight of the ink composition. 9. A static surface tension at 25 ° C. of 20 to 5
The ink composition according to any one of claims 1 to 8, wherein 0 dyne / cm. 10. The ink composition according to claim 1, wherein the pH at 25 ° C. is 6.5 to 11. 11. The ink composition according to claim 1, wherein the viscosity at 25 ° C. is 1 to 5 cps. 12. An ink container comprising the ink composition according to claim 1 incorporated therein. 13. An ink jet recording method using the ink composition according to claim 1. 14. An ink jet recording apparatus using the ink composition according to claim 1. Description: