JP2008231130A - Ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inkjet recording ink which is excellent in safety, develops a color highly on plain paper, has high glossiness on glossy paper, and is excellent in the discharging stability of the ink from an inkjet head. <P>SOLUTION: This inkjet recording ink is characterized by comprising water and a pigment dispersed with a block polymer having an acid value of 50 to 120 mgKOH/g and a weight-average mol.wt. of 20,000 to 120,000. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ink for ink jet recording having excellent stability, high color development on plain paper, high gloss on glossy paper, and excellent ink ejection stability from an ink jet head.

  Inkjet recording is a method of recording characters and figures on the surface of a recording medium by ejecting ink as small droplets from fine nozzles. As an ink jet recording method, an electrostrictive element is used to convert an electrical signal into a mechanical signal, and ink stored in the nozzle head portion is intermittently ejected to record characters and symbols on the surface of the recording medium. A method of recording characters and symbols on the surface of the recording medium, etc. by rapidly heating a part of the ink that is stored in the vicinity of the ejection part to generate bubbles and intermittently ejecting the volume due to the bubbles. It has been put into practical use. The ink used for such ink jet recording has no bleeding, good drying properties, can be printed uniformly on the surface of various recording media, and has multiple colors such as color printing. In the printing of the system, characteristics such as that adjacent colors do not mix are required.

  In conventional inks, many of the inks that use pigments, in particular, have been studied to ensure the print quality by suppressing ink wetting on the paper surface mainly by suppressing penetrability and keeping ink droplets near the paper surface. Has been put to practical use. However, ink that suppresses wetting of paper has a large difference in bleeding due to the difference in the type of paper, and in particular, recycled paper containing various paper components causes bleeding due to differences in the wetting characteristics of the ink for each component. To do. In addition, such an ink has a problem that it takes time to dry the print, and there is a problem that adjacent colors are mixed in multicolor printing such as color printing. Further, an ink using a pigment as a coloring material However, since the pigment remains on the surface of paper or the like, there is a problem that the abrasion resistance is deteriorated.

  In order to solve such problems, attempts have been made to improve the permeability of ink to paper. Addition of diethylene glycol monobutyl ether (see Patent Document 1), Surfynol 465, which is an acetylene glycol-based surfactant. The addition of Nissin Chemical (see Patent Document 2) or the addition of both diethylene glycol monobutyl ether and Surfynol 465 (see Patent Document 3) has been studied. Alternatively, use of ethers of diethylene glycol for ink has been studied (see Patent Document 4).

  Ink-jet recording inks using pigments are generally difficult to improve the ink permeability while ensuring the dispersion stability of the pigment. There are also examples using triethylene glycol monomethyl ether as a pigment (see Patent Document 5) and examples using ethers of ethylene glycol, diethylene glycol or triethylene glycol (see Patent Document 6).

US Pat. No. 5,156,675 US Pat. No. 5,183,502 US Pat. No. 5,196,056 US Pat. No. 2,083,372 Japanese Patent Application Laid-Open No. 56-147861 Japanese Patent Laid-Open No. 9-111165

  However, conventional water-based inks have insufficient print quality, and are often blurred when printed on plain paper such as PPC paper, and color density and color developability are also insufficient. Further, the conventional dispersion is unstable, and when a substance having a hydrophilic part and a hydrophobic part such as a surfactant or glycol ether is present, adsorption / desorption is likely to occur, and the storage stability of the aqueous ink is poor. was there. Ordinary water-based inks need a substance having a hydrophilic part and a hydrophobic part, such as a surfactant and glycol ether, in order to reduce bleeding on paper. Ink that does not use these substances has insufficient permeability to paper, and there is a problem that the type of paper is limited in order to perform uniform printing, which tends to cause deterioration of the printed image.

  Further, additives such as those used in the present invention (acetylene glycol, acetylene alcohol and silicon surfactant, di (tri) ethylene glycol monobutyl ether, (di) propylene glycol monobutyl ether or 1,2- If an alkylene glycol or a mixture thereof is used, long-term storage stability cannot be obtained, and since it has permeability, the colorant penetrates, resulting in a decrease in color development. Further, since the re-dissolvability of the ink is poor, there is a problem that the ink is dried and easily clogged at the tip of the nozzle of the inkjet head. In addition, in the case of pigment ink for ink-jet recording, when glossy paper is used, it generally remains on the surface and thus has low gloss. Further, it is desired that the ink for ink jet has higher color developability on plain paper such as PPC paper and high gloss on glossy paper. However, at present, there is a problem that when the color developability is increased with plain paper, the glossiness with glossy paper is lowered, and when the glossiness with gloss paper is high, the color developability with plain paper is lowered.

  Therefore, the present invention solves such problems, and the object of the present invention is excellent stability, high color on plain paper, high gloss on glossy paper, and ink from an inkjet head. An object of the present invention is to provide an ink for ink jet recording having excellent ejection stability.

  The inkjet ink according to the present invention includes water and a pigment having an acid value of at least 50 mgKOH / g and 120 mgKOH / g and dispersed using a block polymer having a weight average molecular weight of 20,000 to 120,000. .

  The present invention has excellent light resistance, high color on plain paper, high gloss on special paper, and characteristics such as excellent discharge stability of ink from an inkjet head are required. This is based on the result of earnest examination.

  The ink for ink jet recording of the present invention comprises water and a pigment dispersed using a block polymer having an acid value of at least 50 mgKOH / g and 120 mgKOH / g and having a weight average molecular weight of 20,000 to 120,000. To do. Further, when the acid value of the polymer is less than 50 mgKOH / g, dispersion stability cannot be obtained. When it exceeds 120 mgKOH / g, the color developability of plain paper such as PPC paper is lowered. Further, when the polymer has a weight average molecular weight of less than 20,000 and more than 120,000, dispersion stability cannot be obtained.

  Rather than using a random polymer as the polymer used for the dispersion, the color development on plain paper can be improved without reducing the gloss on glossy paper by using a block polymer. As a result, it is possible to realize a paper that has higher color developability on plain paper and high gloss on glossy paper. For this purpose, the block polymer is mainly composed of at least (meth) acrylate and (meth) acrylic acid having an aromatic ring, and the concentration of the (meth) acrylate having the aromatic ring is relatively higher than other components. After the polymerization reaction in the state, it is preferably prepared by performing the polymerization reaction in a state where the concentration of (meth) acrylic acid is higher than the initial stage of the polymerization.

  In the present invention, it is further preferable to use 1,2-alkylene glycol. The 1,2-alkylene glycol is preferably 1,2-hexanediol and / or 1,2-pentanediol. These additions improve the dryness of printing, and even if printing is performed continuously, the previous printing portion is not transferred to the back surface of the next medium, so that high-speed printing is possible. Further, in order to prevent the ink from being blurred even if the printing speed of the ink for ink jet recording according to the present invention is increased or to improve the printing stability, the surface tension of the ink is set in the range of 20 mN / m to 40 mN / m. To do. Therefore, it is also preferable to add at least an alkylene glycol monoalkyl ether. The alkylene glycol monoalkyl ether is preferably an alkylene glycol having 10 or less repeating units and an alkyl ether having 4 to 10 carbon atoms. For example, the alkylene glycol monoalkyl ether is preferably di (tri) ethylene glycol monobutyl ether and / or (di) propylene glycol monobutyl ether.

  In the present invention, it is preferable to use an acetylene glycol surfactant and / or an acetylene alcohol surfactant. By using these surfactants, bleeding on plain paper is particularly reduced, and the dot diameter on the dedicated paper can be expanded to an optimum width.

  The addition amount of the acetylene glycol surfactant and / or acetylene alcohol surfactant is preferably 0.1% or more and 5% or less. In the present invention, it is more preferable to contain at least the above-mentioned acetylene glycol surfactant and / or acetylene alcohol surfactant and 1,2-alkylene glycol. Further, it is preferable to contain di (tri) ethylene glycol monobutyl ether and / or (di) propylene glycol monobutyl ether.

  The addition amount of the aforementioned acetylene glycol surfactant and / or acetylene alcohol surfactant is 0.01% to 0.5%, and the addition amount of 1,2-alkylene glycol is 1% or more. Further preferred. Further, the addition amount of di (tri) ethylene glycol monobutyl ether and / or (di) propylene glycol monobutyl ether is preferably 1.0% or more.

  In this way, by preparing the ink for ink jet recording as described above, an ink jet ink that has high color on plain paper, high gloss on special paper, and excellent ink ejection stability from the ink jet head. Can do.

  As a pigment that can be used in the present invention, carbon black (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, channel black, copper oxide, iron oxide ( Examples include CI pigment black 11), metals such as titanium oxide, and organic pigments such as aniline black (CI pigment black 1), but carbon has a relatively low density and is difficult to settle in water for inkjet use. Black is preferred.

  For color inks, C.I. I. Pigment Yellow 1 (Fast Yellow G), 3, 12 (Disazo Yellow AAA), 13, 14, 17, 24, 34, 35, 37, 42 (Yellow Iron Oxide), 53, 55, 74, 81, 83 (Disazo Yellow HR), 93, 94, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 153, 180, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22 (Brilliant First Scarlet), 23, 31, 38, 48: 2 (Permanent Red 2B (Ba)), 48: 2 (Permanent Red 2B (Ca)), 48 : 3 (Permanent Red 2B (Sr)), 48: 4 (Permanent Red 2B (Mn)), 49: 1, 52: 2, 53: 1, 57: 1 (Brilliant Carmine 6B), 60: 1, 63: 1, 63: 2, 64: 1, 81 (Rhodamine 6G rake), 83, 88, 101 (Bengara), 104, 105, 106, 108 (Cadmium red), 112, 114, 122 (Quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 202, 206, 209, 219, . I. Pigment violet 19, 23, C.I. I. Pigment orange 36, C.I. I. Pigment Blue 1, 2, 15 (phthalocyanine blue R), 15: 1, 15: 2, 15: 3 (phthalocyanine blue G), 15: 4, 15: 6 (phthalocyanine blue E), 16, 17: 1, 56 60, 63, C.I. I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc. can be used.

  As described above, it is preferable to use various dyes and pigments as the colorant, but it is more preferable that the dye is dispersed using a polymer, the dye is permeated into the polymer, or the case where polymer fine particles are used. This is the case of coexistence with a polymer.

  The pigment that can be used in the present invention is dispersed using a disperser. In this case, various commercially available dispersers can be used as the disperser, but non-media dispersion is preferable. Specific examples thereof include a wet jet mill (Genus), a nanomer (Nanomer), a homogenizer (Gorin), an optimizer (Sugino Machine), and a microfluidizer (Microfluidics).

  When used in the inkjet recording ink according to the present invention, the amount added as a pigment is preferably 0.5 to 30%, more preferably 1.0 to 15%. If the addition amount is less than this, the print density cannot be ensured, and if the addition amount is more than this, the viscosity of the ink increases or structural viscosity is generated in the viscosity characteristics, and the ejection stability of the ink from the ink jet head tends to deteriorate. .

  In addition, as a vehicle component of the ink for ink jet recording of the present invention, a surfactant, an organic solvent, a humectant, and the like are used. A surface tension of 20 mN / m or more and 40 mN / m or less is preferably added with at least a surfactant from the viewpoint of expanding the dot diameter printed with the ink jet to an optimum width.

  Further, the ink-jet pigment ink in the present invention is a moisturizer or dissolution aid for the purpose of ensuring its standing stability, stable ejection from the ink-jet head, for improving clogging, or for preventing ink deterioration. Various additives such as chelating agents for trapping metal ions that affect dispersion, penetration control agents, viscosity modifiers, pH adjusters, dissolution aids, antioxidants, antiseptics, antifungal agents, corrosion inhibitors, and dispersion agents Can also be added.

(Example)
Hereinafter, specific embodiments of the present invention will be described. Examples are shown using pigments dispersed using the most preferred polymer, but the present invention is not limited to these examples.

(Preparation of block polymer A)
The reaction vessel equipped with a stirrer, thermometer, reflux tube and dropping funnel was replaced with nitrogen, and then 165 parts of benzyl acrylate, 2 parts of acrylic acid, 2 parts of methacrylic acid, dimethyl-2,2′-azobis (2-methylpropio) 1 part) and 0.3 part of t-dodecyl mercaptan are added and heated to 70 ° C. and polymerized for 1 hour. Next, 50 parts of benzyl acrylate prepared separately, 15 parts of acrylic acid, 5 parts of butyl acrylate, 1 part of t-dodecyl mercaptan, 20 parts of methyl ethyl ketone and 1 part of dimethyl 2,2′-azobis (2-methylpropionate) Is placed in a dropping funnel and the dispersion polymer is polymerized while being dropped into the reaction vessel over 4 hours. Next, methyl ethyl ketone is added to the reaction vessel to prepare a pigment-dispersed polymer solution A which is a 40% concentration block polymer.

(Preparation of block polymer B)
The reaction vessel equipped with a stirrer, thermometer, reflux tube and dropping funnel was purged with nitrogen, and then 105 parts of benzyl acrylate, 30 parts of cyclohexyl acrylate, 2 parts of acrylic acid, 2 parts of methacrylic acid, dimethyl-2,2′-azobis ( 1 part of 2-methylpropionate) and 0.3 part of t-dodecyl mercaptan are added and heated to 70 ° C. and polymerized for 1.5 hours. Next, 50 parts of benzyl acrylate prepared separately, 10 parts of tetrahydrofurfuryl acrylate, 10 parts of acrylic acid, 15 parts of butyl acrylate, 1 part of t-dodecyl mercaptan, 40 parts of methyl ethyl ketone and dimethyl 2,2′-azobis (2- 1 part of methyl propionate) is put into a dropping funnel, and the dispersion polymer is polymerized while dropping into a reaction vessel over 4 hours. Next, methyl ethyl ketone is added to the reaction vessel to prepare a pigment dispersion polymer solution B which is a 40% concentration block polymer.

(Production of Pigment Dispersion 1)
As the pigment dispersion 1, Monarch 880 manufactured by Cabot Corp., US, which is carbon black (PBk7) was used. The acid value was determined by titration with 0.1 mol / L KOH. The weight average molecular weight was measured as the styrene equivalent molecular weight when a part of the dispersion polymer was taken and the solvent was measured as THF using gel permeation chromatography (GPC) of L7100 system manufactured by Hitachi, Ltd.

  Further, 40 parts of the pigment-dispersed polymer solution A, 30 parts of Monarch 880 powder (manufactured by Cabot) that is carbon black, 100 parts of a 0.1 mol / L sodium hydroxide aqueous solution, and 30 parts of methyl ethyl ketone were mixed. Then, using an ultrahigh pressure homogenizer (Ultimizer HJP-25005 manufactured by Sugino Machine Co., Ltd.), the dispersion was performed by passing 15 passes at 200 MPa. The dispersion was transferred to another container, 300 parts of ion exchange water was added, and the mixture was further stirred for 1 hour. And the whole amount of methyl ethyl ketone and a part of water were distilled off using the rotary evaporator, and it neutralized with 0.1 mol / L sodium hydroxide, and adjusted to pH9. The pigment solution was filtered through a 3 μm membrane filter and adjusted with ion-exchanged water to obtain a pigment dispersion 1 having a pigment concentration of 15%.

(Production of Pigment Dispersion 2)
Pigment dispersion 2 was prepared in the same manner as Pigment dispersion 1 except that Pigment Blue 15: 4 (copper phthalocyanine pigment: manufactured by Clariant) was used.

(Production of Pigment Dispersion 3)
Pigment dispersion 3 was prepared in the same manner as pigment dispersion 1 using Pigment Violet 19 (quinacridone pigment: manufactured by Clariant).

(Production of Pigment Dispersion 4)
Pigment Dispersion 3 was prepared in the same manner as Pigment Dispersion 1 using Pigment Yellow 74 (Condensed Azo Pigment: Clariant).

(Preparation of ink for inkjet recording 1)
Table 2 shows examples of compositions suitable for ink jet recording ink. The ink jet recording ink according to the present invention was prepared by mixing the vehicle components shown in Table 2 using the dispersion 1 prepared by the above method. In the remaining amount of water in Table 2, 0.05% of the top side 240 (manufactured by Permachem Asia Co., Ltd.) is used to prevent ink corrosion, and 0.02 of benzotriazole is used to prevent ink jet head member corrosion. %, In order to reduce the influence of metal ions in the ink system, 0.04% each of EDTA (ethylenediaminetetraacetic acid) · 2Na salt was added to ion-exchanged water.

(Comparative Example 1)
In Comparative Example 1, instead of using the block polymer A in Example 1, a random polymer with an equivalent monomer blend was prepared and evaluated. Dispersion 5 using Monarch 880 powder (manufactured by Cabot) for black ink, Dispersion 6 using pigment blue 15: 4 (copper phthalocyanine pigment: Clariant) for cyan ink, magenta ink Pigment Violet 19 (quinacridone pigment: made by Clariant) is used for Dispersion 7 and Pigment Yellow 74 (condensed azo pigment: made by Clariant) is used for Yellow Ink. Ink preparation was performed in the same manner as in Example 1. An example of the composition of Comparative Example 1 is shown in Table 3.

(Comparative Example 2)
In Comparative Example 2, a dispersion was prepared using a polymer in which the amount of acrylic acid was changed in Example 1 and the acid value was changed. However, although an acid value exceeding 200 was dispersible, when 40 and 30 polymers of less than 50 were prepared, none of them became a dispersion. Dispersion 9 using Monarch 880 powder (manufactured by Cabot) for black ink, Dispersion 10 using pigment blue 15: 4 (copper phthalocyanine pigment: made by Clariant) for cyan ink, magenta ink Pigment Violet 19 (quinacridone pigment: made by Clariant) is used as the dispersion 11, and Pigment Yellow 74 (condensed azo pigment: made by Clariant) is used as the dispersion 12 for the yellow ink. Ink preparation was performed in the same manner as in Example 1. An example of the composition of Comparative Example 2 is shown in Table 4.

(Comparative Example 3)
Comparative Example 3 is a polymer in which the molecular weight was changed by changing the amount of reaction time with dimethyl-2,2′-azobis (2-methylpropionate) as a polymerization initiator in Example 1 and changing the reaction temperature. Was used to prepare a dispersion. Dispersion 13 using Monarch 880 powder (manufactured by Cabot) for black ink, Dispersion 14 using pigment blue 15: 1 (copper phthalocyanine pigment: made by Clariant) for cyan ink, magenta ink Pigment Violet 19 (quinacridone pigment: made by Clariant) is used for Dispersion 15 and Pigment Yellow 74 (condensed azo pigment: made by Clariant) is used for Yellow Ink. Ink preparation was performed in the same manner as in Example 1. An example of the composition of Comparative Example 3 is shown in Table 5.

(Evaluation of dispersion stability 1)
Table 1 shows the viscosity change rate (%) and sedimentation rate (%) when ink-jet pigment inks prepared using dispersions having different pigment particle diameters are left at 60 ° C. for 30 days. The dispersion stability is shown as the rate of change in viscosity (%) when each water-based ink is left at 60 ° C. for 30 days. The change in viscosity is measured by an AMVn manufactured by Anton Paar, Germany, at an angle of 60 °, and is shown as 100-% (%) of 1- (value after 30 days) / (initial value).

(Evaluation of plain paper OD and glossy paper glossiness 1)
Xerox 4024 paper manufactured by Xerox Corporation in the United States was used as plain paper, and PM photo paper manufactured by Seiko Epson Corporation was used as glossy paper. The printer used was an ink jet printer EM930C manufactured by Seiko Epson Corporation, and evaluation was performed using a sample printed in a printing mode of 720 dpi for plain paper and 1440 dpi for glossy paper. The OD was measured using GRETAG MACBETH SPECTROSCAN SPM-50 manufactured by GRETAG, USA. The glossiness was measured by measuring the specular glossiness of the recording surface at an incident angle of 60 degrees with a gloss checker IG-320 manufactured by Horiba, Ltd., and taking the average of 5 times for each recording paper. The media was printed with photo 720 dpi using PM photo paper manufactured by Seiko Epson Corporation and the printer using EM930C manufactured by Seiko Epson Corporation. The results are shown in Table 1.

(Measurement of ejection stability 1)
Using PX-V600 manufactured by Seiko Epson Corporation as an inkjet printer, Microsoft Xerox P paper A4 size manufactured by Fuji Xerox Co., Ltd. at 35 ° C and 35% atmosphere, with a character size of 11 in Microsoft Word and MSP Gothic at a rate of 4000 characters / page The page was printed and evaluated. AA when there is no printing disorder at all, A with printing disorder at one place, B with printing disorder at 2-3 places, C at 4-5 printing disorders, and 6 or more printing disorders The results are shown in Table 1 with D as the result.

(Production of Pigment Dispersion 17)
As the pigment dispersion 17, Monarch 880 manufactured by Cabot Corp. of USA was carbon black (PBk7). The acid value was determined by titration with 0.1 mol / L KOH. The weight average molecular weight was measured as the styrene equivalent molecular weight when a part of the dispersion polymer was taken and the solvent was measured as THF using gel permeation chromatography (GPC) of L7100 system manufactured by Hitachi, Ltd.

  Further, 40 parts of the above pigment dispersion polymer solution B, 30 parts of Monarch 880 powder (manufactured by Cabot) as carbon black, 100 parts of a 0.1 mol / L sodium hydroxide aqueous solution, and 30 parts of methyl ethyl ketone were mixed. Then, using an ultrahigh pressure homogenizer (Ultimizer HJP-25005 manufactured by Sugino Machine Co., Ltd.), the dispersion was performed by passing 15 passes at 200 MPa. The dispersion was transferred to another container, 300 parts of ion exchange water was added, and the mixture was further stirred for 1 hour. And the whole amount of methyl ethyl ketone and a part of water were distilled off using the rotary evaporator, and it neutralized with 0.1 mol / L sodium hydroxide, and adjusted to pH9. The pigment solution was filtered through a 3 μm membrane filter and adjusted with ion-exchanged water to obtain a pigment dispersion 17 having a pigment concentration of 15%.

(Production of Pigment Dispersion 18)
First, Dispersion 19 was prepared in the same manner as Dispersion 17 using Pigment Blue 15: 4 (copper phthalocyanine pigment: manufactured by Clariant).

(Production of Pigment Dispersion 19)
First, Dispersion 19 was prepared in the same manner as Dispersion 17 using Pigment Red 122 (dimethylquinacridone pigment: Clariant).

(Production of pigment dispersion 20)
First, Dispersion 20 was prepared in the same manner as Dispersion 17 using Pigment Yellow 180 (diketopyrrolopyrrole pigment: manufactured by Clariant).

(Preparation of inkjet ink 2)
Examples of compositions suitable for ink jet recording ink are shown in Table 7 below. The ink for inkjet recording was prepared in the same manner as in Example 1.

(Comparative Example 4)
In Comparative Example 4, instead of using the block polymer B in Example 2, a random polymer with an equivalent monomer blend was prepared and evaluated. Dispersion 21 using Monarch 880 powder (manufactured by Cabot) for black ink, Dispersion 22 using pigment blue 15: 4 (copper phthalocyanine pigment: Clariant) for cyan ink, magenta ink Pigment Violet 19 (quinacridone pigment: made by Clariant) is used as dispersion 23, and Pigment Yellow 74 (condensed azo pigment: made by Clariant) is used for yellow ink as dispersion 24. Ink preparation was performed in the same manner as in Example 2. An example of the composition of Comparative Example 5 is shown in Table 8.

(Comparative Example 5)
In Comparative Example 5, a dispersion was prepared using a polymer in which the amount of acrylic acid was changed in Example 2 and the acid value was changed. However, although an acid value exceeding 200 was dispersible, when 40 and 30 polymers of less than 50 were prepared, none of them became a dispersion. Dispersion 25 using Monarch 880 powder (manufactured by Cabot) for black ink, Dispersion 26 using pigment blue 15: 4 (copper phthalocyanine pigment: made by Clariant) for cyan ink, magenta ink Pigment Red 122 (dimethylquinacridone pigment: manufactured by Clariant) is used as dispersion 27, and Pigment Yellow 180 (diketopyrrolopyrrole pigment: manufactured by Clariant) is used as dispersion 28 for yellow ink. Ink preparation was performed in the same manner as in Example 2. An example of the composition of Comparative Example 6 is shown in Table 9.

(Comparative Example 6)
In Comparative Example 6, a dispersion was prepared using sodium persulfate, which is a polymerization initiator in Example 2, and a polymer having a changed molecular weight while changing the amount of reaction temperature and reaction time. Dispersion 29 using Monarch 880 powder (manufactured by Cabot) for black ink, Dispersion 30 using pigment blue 15: 4 (copper phthalocyanine pigment: made by Clariant) for cyan ink, magenta ink Pigment Red 122 (dimethylquinacridone pigment: manufactured by Clariant) is used as a dispersion 31 and Pigment Yellow 180 (diketopyrrolopyrrole pigment: manufactured by Clariant) is used as a dispersion 32 for yellow ink. Ink preparation was performed in the same manner as in Example 1. An example of the composition of Comparative Example 7 is shown in Table 10.

(Evaluation of dispersion stability 2)
Evaluation of dispersion stability was carried out in the same manner as in Example 1. The results are shown in Table 6.

(Evaluation of plain paper OD and glossy gloss 2)
Evaluation of plain paper OD and glossy paper gloss was carried out in the same manner as in Example 1. The results are shown in Table 6.

(Discharge stability measurement 2)
The ejection stability was measured in the same manner as in Example 1. The results are shown in Table 6.

Claims (4)

  An ink for ink jet recording comprising water and a pigment dispersed using a block polymer having an acid value of at least 50 mgKOH / g and 120 mgKOH / g and having a weight average molecular weight of 20,000 to 120,000.   The block polymer is composed mainly of (meth) acrylate having at least an aromatic ring and (meth) acrylic acid as a main component, and is first subjected to a polymerization reaction in a state where the concentration of the (meth) acrylate having an aromatic ring is relatively higher than other components. 2. The ink for ink jet recording according to claim 1, wherein the ink is prepared by a polymerization reaction in a state where the concentration of (meth) acrylic acid is higher than that in the initial stage of polymerization.   The ink for inkjet recording according to claim 1, wherein 1,2-alkylene glycol is used.   The ink for inkjet recording according to any one of claims 1 to 3, wherein an acetylene glycol surfactant and / or an acetylene alcohol surfactant is used.