JP2020059786A - Pigment ink for inkjet recording, printed matter and production method of printed matter - Google Patents

Abstract

To provide a pigment ink for inkjet recording which is capable of preventing occurrence of non-discharge of the pigment ink from an ink discharge head caused by viscosity rise of the pigment ink during print stop and capable of preventing of printing failure such as non-coloration of an edge part of a printed image formable by the pigment ink firstly discharged when the printing is resumed.SOLUTION: The present invention relates to a pigment ink for inkjet recording which is characterized in that, in a production process of a printed matter using an inkjet recording device, a ratio of color optical density of an image formed by a second ink drop when the ink is redischarged after one minute from a time when the inkjet recording device stopped to discharge the ink and the color optical density of an image formed with tenth ink drop is 0.75 to 1.5.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to an inkjet recording ink that can be used for producing printed matter.

  With the recent growth of the print-on-demand market, the inkjet recording method is required to achieve high-speed printing at a level comparable to that of the lithographic printing method. As a method for realizing high-speed printing, for example, a method using a so-called line head type inkjet recording device in which an ink ejection head does not move during printing is known.

  However, since the line head type ink discharge head cannot perform flushing when printing a recording medium sheet by sheet, for example, when the print stop time exceeds about 1 minute, the water contained in the ink evaporates. As a result, the viscosity of the ink rises, the ink is not ejected from the ink ejection head, or the direction in which the ink is ejected is bent, so that the ink droplet lands at the position on the recording medium that should originally land. In some cases, problems such as inability (flying bend) occurred.

  Further, even if the ink can be ejected, the color material contained in the ink in the head may be slightly separated during the printing stop. Therefore, when the printing is resumed after the printing is stopped, the color density of the image formed by the first few drops of ink becomes very low, and the end portion of the printed image is not colored or is colored. However, printing defects such as very faint colors tend to occur, and as a result, the quality of the printed image may be degraded.

  In particular, while application of the inkjet ink recording method is being considered for printing barcodes and the like, it is formed by the first and second drops of ink ejected first when printing is resumed after the printing is stopped. Since it is undeniable that the low color density of the formed image may cause misrecognition of bar code reading, the industry has also shown that the images formed by the first and second drops of ink are also colored. It is required to form a clear image with high density.

  The ink capable of solving the above-mentioned problems includes, for example, a dye, an ethylene oxide adduct of a silicon-based surfactant and acetylene glycol, and a liquid medium, and an ethylene oxide addition of the acetylene glycol of the silicon-based surfactant. There is known an ink characterized by having a mass ratio of 1/5000 or more to less than 1/20 (see, for example, Patent Document 1).

  However, with the ink, after the printing is stopped, the color density of the image formed by the first drop, particularly the second drop of the ink ejected when printing is restarted is increased to a practically sufficient level. There were times when you couldn't.

  Further, the pigment ink is formed by the first drop of the pigment ink, particularly the second drop of ink, because the color material contained in the ink in the head is easily separated during the printing stop, as compared with the dye ink. It was difficult to increase the color density of the formed image and suppress the deterioration of the image quality of the printed image.

JP-A-2002-80768

  The problem to be solved by the present invention is to prevent the occurrence of non-ejection of the pigment ink from the ink ejection head due to the increase in the viscosity of the pigment ink during printing stoppage, and for the first ejection when the printing is restarted. Inkjet recording that can prevent the occurrence of printing defects such as uncolored edges of printed images that can be formed by pigment inks that are formed, or very pale colors even when they can be colored, and print disturbances. To provide a pigment ink for printed matter, a printed matter, and a method for producing a printed matter.

The present invention provides a second ink drop (X ² ) when ink is ejected again one minute after the ink jet recording apparatus stops ejecting ink in a process for producing a printed matter using the ink jet recording apparatus. Is the photographic paper Crispia high gloss (Seiko Epson Corporation, KA420SCKR), and the color density (D ² ) of the image (Y ² ) formed by landing and the 10th ink drop (X ¹⁰ ) are photographic paper Crispia high gloss. gloss (manufactured by Seiko Epson Corporation, KA420SCKR) ratio of the color density ^{(D 10)} for landed the image formed on the ^{(Y 10)} [color density ^(D 2) / color density ^{(D 10)]} of 0.75 The problem is solved by a pigment ink for ink jet recording, which is characterized by being 1.5 to 1.5.

Further, the present invention is a method for producing a printed matter, which comprises a step [1] of ejecting the inkjet recording pigment ink onto a recording medium using an inkjet recording apparatus, wherein the inkjet recording apparatus stops the ejection of ink. After 1 minute from the time when the ink was ejected again, the second ink droplet (X ² ) landed on the recording medium and the color density (D ² ) of the image (Y ² ) formed and 10 Ratio of the color ink density (X ¹⁰ ) to the color density (D ¹⁰ ) of the image (Y ¹⁰ ) formed by landing the ink drop (X ¹⁰ ) on the recording medium [color density (D ² ) / color density (D ¹⁰ )]. The above problem is solved by a method for producing a printed matter and a printed matter characterized in that

  By using the inkjet recording pigment ink of the present invention, for example, it is possible to prevent the non-ejection of the pigment ink from the ink ejection head due to the increase in the viscosity of the pigment ink during printing stop, and the first time when the printing is restarted. The edges of the printed image that can be formed by the first and second drops of the pigment ink ejected onto the surface are not colored, or even if they are colored, the colors are very pale or the printing is disturbed. It is possible to prevent printing defects.

The print image used for evaluation of ink is shown. The part of the said print image used when calculating the ratio of coloring density is shown. The part of the said printed image used for evaluation of ink is shown.

The pigment ink for ink jet recording of the present invention is a second drop when the ink is ejected again one minute after the ink ejection of the ink jet recording apparatus is stopped in the manufacturing process of a printed matter using the ink jet recording apparatus. The color density (D ² ) of the image (Y ² ) formed by the ink droplet (X ² ) landing on the photo paper Crispia high gloss (Seiko Epson Corporation, KA420SCKR) and the 10th ink droplet (X ^10). ) Is a ratio [coloring density (D ² ) / coloring density (D ¹⁰ ) of the color density (D ¹⁰ ) of the image (Y ¹⁰ ) formed by landing on the photo paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Corporation). )] Is 0.75 to 1.5. By using the inkjet recording pigment ink, for example, it is possible to prevent the non-ejection of the pigment ink from the ink ejection head due to the increase in the viscosity of the pigment ink while the printing is stopped, and to eject the pigment ink first when printing is restarted. The edge of the printed image that can be formed by the second drop of pigment ink is not colored, or even if it is colored, it may be a very pale color, or printing defects such as disturbed printing may occur. Can be prevented.

  Here, in the ink having the ratio of less than 0.75, the color of the end portion of the print image becomes light, and as a result, the contour of the print image may be unclear. On the other hand, in the ink having the above ratio of more than 1.5, the color of the end portion of the printed image becomes darker than the others, and as a result, uneven density of the printed image may occur.

The ratio [color density (D ² ) / color density (D ¹⁰ )] refers to a value calculated by the following method.

  First, in a 25 ° C. environment, a photo paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Corporation) is prepared as a recording medium, and an ink jet printing apparatus equipped with an ink jet head having a plurality of ejection nozzles (amount of one drop of ink) Is adjusted to 12 pl) to perform 100% solid printing in a range of 2 cm in length and 10 cm in width of the recording medium.

  After the completion of the printing, the ejection of ink is stopped, and then the ink is left for 1 minute.

  After the leaving, in order to create a preset print image (FIG. 1), 89 of the plurality of ejection nozzles provided in the inkjet printing device are provided on the photo paper Crispia high gloss (Seiko Epson Corporation, KA420SCKR). A printed matter is obtained by ejecting 16 droplets of ink droplets (the amount of each droplet is 12 pl) from the ejection nozzles.

  The image of the printed matter is photographed using an optical microscope (manufactured by KEYENCE, magnification 30 times), and the image is taken into a computer.

Next, of the printed matter (FIG. 1), an image printed in a range indicated by 2 in FIG. 2 (from 16 dots formed by 1 to 16 drops of ink ejected from one ejection nozzle) Image), image processing software (Image J) is used, and the second drop of the image is ejected again 1 minute after the ink jet recording apparatus stops ejecting the ink. Image density (D ² ) of the image (Y ² ) (4 in FIG. ² ) formed by the ink droplet (X ² ) of FIG. 2 and the image (Y ¹⁰ ) formed by the ^10th ink droplet (X ¹⁰ ). ) (5 in FIG. 2) and the color density (D ¹⁰ ) are measured.

Next, the ratio [coloring density (D ² ) / coloring density (D ¹⁰ )] is calculated based on the values of the above-mentioned color density (D ² ) and color density (D ¹⁰ ).

In the image processing software (Image J), the image captured by the method was binarized, and then "Light Background" was selected to remove light unevenness and noise in the image. From the image after the processing, an image that measures the color density ^{(Y 2)} and image ^{(Y 10)} were selected with a linear tool, is displayed by selecting the "Plotprofile" the image ^{(Y 2)} and image ( Among the peaks corresponding to each of Y ¹⁰ ), the difference between the lowest value and 255 is defined as the coloring density (D ² ) and the coloring density (D ¹⁰ ), respectively.

In the ink of the present invention, the ratio [coloring density (D ² ) / coloring density (D ¹⁰ )] preferably satisfies 0.75 to 1.5, and is in the range of 0.85 to 1.2. It is more preferable to use the one for preventing the color of the end portion of the printed image from becoming light.

Further, as the pigment ink for inkjet recording of the present invention, the first ink droplet (X ¹ ) when the ink is ejected again one minute after the ink ejection of the inkjet recording apparatus is stopped is photographed. Paper Crispia High gloss (Seiko Epson Corporation, KA420SCKR) landing image (Y ¹ ) (3 in FIG. 2) formed color density (D ¹ ) and 10th ink drop (X ¹⁰ ) There photo paper CRISPIA high gloss (manufactured by Seiko Epson Corporation, KA420SCKR) landed the image formed on the ^{(Y 10)} color density (5 in FIG. 2) ratio [color density and ^{(D 10) (D} 1) / Color density (D ¹⁰ )] is preferably in the range of 0.4 to 1.5, and 0.5 to 1.2 is used for the ink ejection for 1 minute. Stop After, C, color of the end portion of the printed image can be prevented that the thinner, more preferable since it is possible to obtain a clear printed image free from blurring or color unevenness.

Further, as the ink of the present invention, one minute after the ink jet recording apparatus stops the ink ejection, the third ink droplet (X ³ ) when the ink is ejected again is photographic paper Crispia high gloss ( The color density (D ³ ) of the image (Y ³ ) formed by landing on the KA420SCKR manufactured by Seiko Epson Co., Ltd. and the tenth ink drop (X ¹⁰ ) are photographic paper Crispia high gloss (manufactured by Seiko Epson Co., Ltd.). , the ratio [color density ^(D 3) / color density ^{(D 10)]} and concentration of color density ^{(D 10)} of the image that is landed on KA420SCKR) forming ^{(Y 10)} is 0.6 to 1.5 It is preferable to satisfy the above condition, and it is more preferable to use the one within the range of 0.85 to 1.2 in order to prevent the color of the end portion of the printed image from becoming light.

  In addition, the ink of the present invention has a lower limit of surface tension at 25 ° C. of 20 mN / m or more, more preferably 25 mN / m or more, and further preferably 28 mN / m or more. On the other hand, the upper limit of the surface tension of the water-based ink at 25 ° C. is 40 mN / m or less, preferably 35 mN / m or less, and more preferably 32 mN / m or less.

  The ink having a surface tension in the above range prevents ink overflow from the nozzles, etc., so that the printing is stopped for a certain period of time, and when the printing is restarted, non-ejection of the first droplet ejected or flight deflection is prevented. It can be effectively prevented.

The surface tension of the ink means a value measured under the following conditions using an automatic surface tension meter to which the Wilhelmi method is applied. According to the Wilhelmy method, the static surface tension and the dynamic surface tension can be measured, but the surface tension of the ink in the present invention represents the value of the static surface tension.
Measuring device: Automatic surface tensiometer (Kyowa Interface Science Co., Ltd., CBVP-Z type)
Measurement temperature: 25 ° C
Stylus: platinum plate

  As the pigment ink for inkjet recording, for example, one containing a surfactant, a pigment and an aqueous medium can be used.

The surfactant is used for adjusting the ratio [coloring density (D ² ) / coloring density (D ¹⁰ )] of the pigment ink for inkjet recording of the present invention within a range of 0.75 to 1.5. As a result, it is possible to obtain a pigment ink for ink jet recording having excellent wettability with respect to a recording medium having a low ink absorptivity and having poor absorbency or non-absorbency.

  As the surfactant, for example, various anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants and the like can be used.

  Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, higher fatty acid ester sulfate ester salt, higher fatty acid ester sulfonate, and higher alcohol. Sulfate ester salts and sulfonates of ethers, higher alkylsulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates and the like. As specific examples of these, dodecylbenzene sulfonate, isopropyl naphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, dibutylphenylphenol bis It can be used, such as Hong salt.

  Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and glycerin fatty acid. Ester, polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkylalkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol , Polyethylene glycol polypropylene glycol block copolymer, polyether modified white It can be used litter size polymer.

Among them, it is preferable to use an acetylene-based surfactant as the surfactant, and it is more preferable to use an acetylene-based surfactant (A) having 10 or more carbon atoms in the main chain, The use of an acetylene-based surfactant having 12 or more atoms allows the ratio [coloring density (D ² ) / coloring density (D ¹⁰ )] to be 0.75 to 1.5, more preferably 0.85 to 1.55. It is more preferable to adjust within the range of 1.2, and as a result, to prevent the color of the end portion of the printed image from becoming light.

  Specific examples of the acetylene-based surfactant (A) having 10 or more carbon atoms in the main chain include commercially available "Surfynol 104PG-50", "Surfynol 420", and "Surfynol 440". , "Surfynol 465", "Surfynol 485", "Surfynol SE", "Surfynol SEF", "Surfynol DF110D", Dynol 604 "," Dynol 607 "(manufactured by EVONIK) and "Acetylenol E13T" (manufactured by Kawaken Fine Chemical Co., Ltd.) or the like can be used. Among them, as the acetylene-based surfactant (A), it is preferable to use an acetylene-based surfactant having a polyoxyethylene structure and having 12 or more carbon atoms in the main chain so that the color of the end portion of the printed image becomes thin. It is more preferable to prevent the occurrence of The upper limit of the number of carbon atoms of the acetylene-based surfactant having 12 or more carbon atoms in the main chain having the polyoxyethylene structure is preferably 20 or less, preferably 15 or less, and 13 or less. Is particularly preferred.

  Examples of the acetylene-based surfactant having a polyoxyethylene structure having 12 or more carbon atoms in the main chain include commercially available "Safynol DF110D", "Dynol 604", "Dynol 607" (manufactured by EVONIK). ) Can be used.

  As the surfactant, it is preferable to use one having an HLB in the range of 4 to 20, and it is preferable to use one having an HLB in the range of 8 to 20 so that the color at the edge of the printed image becomes light. It is more preferable for prevention.

The surfactant is preferably used in the range of 0.1 to 5% by mass with respect to the total amount of the pigment ink for inkjet recording, and is not ejected in the range of 0.1 to 2% by mass. And it is easy to adjust the ratio [coloring density (D ² ) / coloring density (D ¹⁰ )] within the range of 0.75 to 1.5, and as a result, the color at the edge of the printed image is prevented. It is more preferable to prevent thinning.

  The pigment that can be used in the inkjet recording pigment ink is not particularly limited, and an organic pigment or an inorganic pigment that is usually used in an aqueous gravure ink or an aqueous inkjet recording ink can be used.

  As the organic pigment and the inorganic pigment, both non-acid-treated pigments and acid-treated pigments can be used.

  As the inorganic pigment, for example, iron oxide, carbon black produced by a method such as a contact method, a furnace method, a thermal method, or the like can be used.

  Examples of the organic pigment include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (eg, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazines). Pigments, thioindigo pigments, isoindolinone pigments, quinofuraron pigments, etc.), lake pigments (eg, basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black and the like can be used.

  Among the above pigments, carbon black that can be used for black ink is No. 1 manufactured by Mitsubishi Chemical Corporation. 2300, No. 2200B, No. 900, No. 960, No. 980, No. 33, No. 40, No. 45, No. 45L, No. 52, HCF88, MA7, MA8, MA100, etc. are Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc., made by Colombia; , Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc., Color Black FW1, the same FW2, the same FW2V, the same FW18, the same FW200, the same S150, the same S160, the same S170, and P170, the same S170, Print, and S170, Prit. V, 1400U, Special Black 6, 5, 5, 4A, NIPEX150, NIPEX160, NIPEX170, NIPEX180 and the like can be used.

  In addition, specific examples of pigments that can be used in the yellow ink include C.I. I. Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 174, 180, 185 and the like. In addition, specific examples of pigments usable in magenta ink include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 146, 176, 184, 185, 202, 209, 269, 282, etc. C. I. Pigment Violet 19 and the like. In addition, specific examples of pigments that can be used for cyan ink include C.I. I. Pigment Blue 1, 2, 3, 15, 15: 3, 15: 4, 16, 22, 60, 63, 66 and the like.

  The pigment is preferably used in the range of 1% by mass to 20% by mass with respect to the total amount of the pigment ink for inkjet recording, and is preferably used in the range of 2% by mass to 10% by mass. Particularly preferable in suppressing non-ejection and flight bending due to nozzle clogging when ink ejection is restarted due to ink drying, etc., and maintaining excellent dispersion stability, and improving print density of printed matter. .

  Further, as the pigment, a self-dispersion pigment, and those in which the pigment is dispersed in water or the like by a dispersant such as a polymer dispersant, the pigment can be used in water or the like by the dispersant. It is more preferable to use the dispersed particles in order to prevent the color of the edge portion of the printed image from becoming light.

  As the aqueous medium that can be used for the pigment ink for inkjet recording, water alone or a mixed solvent of water and an organic solvent can be used.

  As the water, specifically, deionized water, ultrafiltered water, reverse osmosis water, distilled water, or other pure water, or ultrapure water can be used.

  The aqueous medium is preferably used in the range of 30% by mass to 70% by mass, and preferably in the range of 40% by mass to 60% by mass with respect to the total amount of the pigment ink for inkjet recording. It is particularly preferable for maintaining stable dispersion stability and suppressing non-ejection and flight bending due to nozzle clogging when the ejection of the ink is restarted.

  Examples of the organic solvent that can be used in combination with the water as the aqueous medium include ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; methanol, ethanol, isopropyl alcohol, 1-propanol, and 2-propanol. , 2-methyl-1-propanol, 1-butanol, 2-butanol, 2-methoxyethanol and like alcohols; tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane and like ethers; dimethylformamide, N- Glycols such as methylpyrrolidone, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol; butanediol Diols such as pentanediol, hexanediol and diols homologous thereto; glycol esters such as propylene glycol laurate; diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol ether, dipropylene glycol ether, and Glycol ethers such as cellosolve containing triethylene glycol ether; sulfolane; lactones such as γ-butyrolactone; lactams such as N- (2-hydroxyethyl) pyrrolidone; glycerin, diglycerin, polyglycerin, diglycerin fatty acid ester, Polyoxypropylene (n) polyglyceryl ether represented by the general formula (1), Polio represented by the general formula (2) Xyethylene (n) polyglyceryl ether etc. can be used individually or in combination of 2 or more types.

  M, n, o, and p in the general formula (1) and the general formula (2) each independently represent an integer of 1 to 10.

  Examples of the organic solvent include 3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butyl acetate, ethylene glycol monomethyl ether, ethylene glycol mono Ethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol-t-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether acetate, Diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol die Ether, dipropylene glycol dimethyl ether, 4-methoxy-4-methyl-2-pentanone, it can be combined using ethyl lactate and the like alone or in combination.

  Among them, the water-soluble organic solvent is, for example, glycerin, a glycerin derivative, or diglycerin for suppressing non-ejection and flight bending due to nozzle clogging when ink ejection is restarted due to drying of pigment ink near the nozzle. It is preferable to use at least one organic solvent selected from the group consisting of and a diglycerin derivative.

  In addition, as the water-soluble organic solvent, it is possible to maintain good dispersion stability of the ink and to suppress deterioration of an ink ejection nozzle included in an inkjet device due to the influence of the solvent contained in the ink, and In order to prevent the color of the edges from becoming light, it is preferable to use a water-soluble organic solvent having a hydrogen bond term δH of HSP (Hansen solubility parameter) in the range of 6 to 20.

  Specific examples of the water-soluble organic solvent having a hydrogen bond term of HSP within the above range include 3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol, ethylene glycol monomethyl ether, and ethylene glycol mono. Ethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol-t-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether and propylene glycol monopropyl ether are preferable, and 3 is more preferable. -Methoxy-1-butanol and 3-methyl-3-methoxy-1-butanol.

  As the pigment ink for inkjet recording of the present invention, in addition to the above-mentioned ones, those containing a pigment dispersant, a binder resin, a compound having a urea bond, and the like can be used if necessary.

  Examples of the pigment dispersant include polyvinyl alcohols, polyvinylpyrrolidones, acrylic resins such as acrylic acid-acrylic acid ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid. -Styrene-acrylic resin such as acrylic acid ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer, styrene-maleic acid copolymer A combined resin, an aqueous resin of a styrene-maleic anhydride copolymer, a vinylnaphthalene-acrylic acid copolymer, and a salt of the aqueous resin can be used. As the pigment dispersant, Ajinomoto Fine Techno Co., Ltd.'s Azisper PB series, Big Chemie Japan's Disperbyk series, BASF's EFKA series, Nippon Lubrizol's SOLSPERSE series, Evonik's product The TEGO series etc. of can be used.

  Examples of the binder resin include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinylpyrrolidone, acrylic resin, urethane resin, dextran, dextrin, color genin (κ, ι, λ), agar, pullulan, water-soluble polyvinyl butyral, hydroxy. One kind or several kinds of ethyl cellulose, carboxymethyl cellulose and the like can be used in combination. Above all, it is preferable to use an acrylic resin as the binder resin, and it is preferable to use an acrylic resin having an amide group.

  In the ink containing the binder resin, even when the ink at the ink ejection port is solidified due to the evaporation of the solvent due to the drying, the coagulated product is easily dispersed in the ink by the flow of the ink again at the ejection port. Excellent dispersibility (redispersibility). As a result, when ejecting from the inkjet head, even if the ejection is interrupted for a certain period of time and then restarted, it is difficult to cause flight deflection of the ejected droplets or blockage of the ejection port, and it is possible to reduce the image quality at the end of the printed matter. Can be prevented.

  The binder resin is preferably used in the range of 2% by mass to 10% by mass with respect to the total amount of the pigment ink for inkjet recording, and is preferably used in the range of 2% by mass to 6% by mass in the vicinity of the nozzle. It is particularly preferable in suppressing non-ejection and flight bending due to nozzle clogging when ink ejection is restarted due to drying of the pigment ink.

  Examples of the compound having a urea bond include urea, ethylene urea, propylene urea, diethyl urea, thiourea, N, N-dimethyl urea, hydroxyethyl urea, hydroxybutyl urea, ethylene thiourea and diethyl thiourea.

  The compound having a urea bond is preferably used in the range of 1% by mass to 20% by mass, and preferably in the range of 2% by mass to 15% by mass, based on the total amount of the pigment ink for inkjet recording. It is particularly preferable for suppressing non-ejection and flight bending due to nozzle clogging when ink ejection is restarted due to drying of pigment ink in the vicinity of the nozzle.

  In addition, an antiseptic agent, a viscosity adjusting agent, a pH adjusting agent, a chelating agent, a plasticizer, an antioxidant, an ultraviolet absorber and the like can be added if necessary.

  The pigment ink for inkjet recording of the present invention can be produced by mixing, for example, the above-mentioned surfactant, pigment, aqueous medium, pigment dispersion resin, binder resin, compound having a urea bond and the like.

  At the time of the mixing, for example, a bead mill, an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a roll mill, a sand mill, a sand grinder, a dyno mill, a dispermat, an SC mill, a nanomizer, or the like can be used.

  As the method for producing the pigment ink for inkjet recording, more specifically, a pigment, a surfactant, an aqueous medium and, if necessary, optional components such as the binder resin and the compound having a urea bond are mixed at once. And a method of manufacturing by stirring.

  The method for producing the pigment ink for inkjet recording of the present invention includes, for example, <1> a pigment dispersion containing the pigment in a high concentration by mixing the pigment dispersant such as the polymer with the pigment and an aqueous medium. a step of producing a, <2> a step of producing a composition b by mixing the compound having a urea bond with an aqueous medium, if necessary, <3> containing the binder resin, the aqueous medium and the like And the method of <4> mixing the pigment dispersion a, the composition b, and the composition c.

  The pigment ink for inkjet recording obtained by the above method is preferably subjected to a centrifugal treatment or a filtration treatment, if necessary, in order to remove impurities mixed in the ink.

  The pH of the pigment ink for inkjet recording of the present invention improves the storage stability and the ejection stability of the ink and is a non-absorbent recording medium having no ink absorbability, or a low water absorbability of the ink. In order to improve wetting and spreading when printed on an absorptive recording medium, print density, and scratch resistance, it is preferably 7.0 or more, more preferably 7.5 or more, still more preferably 8.0 or more. is there. The upper limit of the pH of the ink suppresses deterioration of members (for example, an ink ejection port, an ink flow path, etc.) that configure the ink application or ejection device, and reduces the influence when the ink adheres to the skin. In addition, it is preferably 11.0 or less, more preferably 10.5 or less, still more preferably 10.0 or less.

  INDUSTRIAL APPLICABILITY The pigment ink for inkjet recording of the present invention is a recording medium having excellent ink absorbability such as copy paper (PPC paper) generally used in copying machines, a recording medium having an ink absorption layer, and an ink. It is possible to print on a non-absorptive recording medium having no absorbability or a hardly-absorbing recording medium having low ink water absorption. In particular, the ink can be suitably printed even on a recording medium that is non-ink-absorbent or hard to absorb.

Specific examples of the recording medium include plain paper, cloth, corrugated board, wood, ink jet dedicated paper, art paper, coated paper, lightweight coated paper, lightly coated paper, plastic film, or water absorption amount of 10 g / m ² or less. Corrugated cardboard with layers can be used.

  As the hardly-absorbent recording medium, a recording medium having a water absorption amount of 10 g / m 2 or less of the recording medium at a contact time of 100 msec between the recording medium and water may be used in combination with the ink. It is preferable for obtaining a printed matter having more excellent scratch resistance and water resistance.

  The amount of water absorption was measured by using an automatic scanning liquid absorption meter (KM500win, manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions of 23 ° C. and 50% relative humidity at a pure water contact time of 100 ms. The amount of transition was measured, and the water absorption amount was 100 ms. The measurement conditions are shown below.

[Spiral Method]
Contact Time: 0.010 to 1.0 (sec)
Pitch: 7 (mm)
Length per sampling: 86.29 (degree)
Start Radius: 20 (mm)
End Radius: 60 (mm)
Min Contact Time: 10 (ms)
Max Contact Time: 1000 (ms)
Sampling Pattern: 50
Number of sampling points: 19
[Square Head]
Slit Span: 1 (mm)
Width: 5 (mm)

  Examples of the recording medium having ink absorbability include plain paper, cloth, cardboard, wood and the like. Examples of the recording medium having the absorbing layer include inkjet-dedicated paper and the like, and specific examples include PICTRICO PRO Photo Paper of PICTRICO CORPORATION.

  Non-absorbent recording media with low ink absorbency include corrugated cardboard with a colored layer that does not easily absorb the solvent in the ink on the surface, art paper such as printing paper, coated paper, lightweight coated paper, light coating. Craft paper can be used. These hard-to-absorb recording media have a coating layer formed by coating a coating material on the surface of a high-quality paper or a neutral paper, which is mainly composed of cellulose and which is not generally surface-treated. ) Manufactured by Nippon Paper Industries Co., Ltd. and “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., “OK Coat L” manufactured by Oji Paper Co., Ltd., and “Aurora” manufactured by Nippon Paper Industries Co., Ltd. "L" and other light-weight coated paper (A3), Oji Paper Co., Ltd.'s "OK top coat + (basis weight 104.7 g / m2, water absorption at contact time 100 msec (the following water absorption is the same)) 4.9 g / M2) "," Aurora Coat "manufactured by Nippon Paper Industries Co., Ltd., Finese Gloss manufactured by UPM (115 g / m2 manufactured by UPM, water absorption 3.1 g / m2) and Fines Matt (115 g / m2, water absorption measured). 4.4 g / m2 ) And other coated papers (A2, B2), art paper (A1) such as "OK Kinto +" manufactured by Oji Paper Co., Ltd. and "Tokuryo Art" manufactured by Mitsubishi Paper Mills Co., Ltd., and other plastic films are used. Can be used.

  Examples of a method for producing a printed matter using the inkjet recording pigment ink and the recording medium include a method of ejecting the inkjet recording pigment ink onto the recording medium in an inkjet recording apparatus.

  As an inkjet recording device that can be used when manufacturing the printed matter, as a head for ejecting ink, it can be used in any of the devices having a line head or a scan head, the ink of the present invention, among others, It has a line head, and is effective when using an apparatus capable of printing on a recording medium of a sheet. Specifically, in printing using an apparatus that has a line head and is capable of printing on a sheet of recording medium, recovery of ink flushing and the like that is generally performed when printing with a rotary recording medium or a scan method. It is necessary to be able to perform good operation even when the operation cannot be performed and ink ejection is restarted after printing is stopped for a certain period of time. Therefore, by using the ink of the present invention, even when printing is performed using a device having a line head and capable of printing on a sheet of recording medium, it is possible to prevent print defects when ink ejection is restarted. It is possible to obtain an excellent printed matter.

  By the way, when the ink of the present invention is printed on the recording medium by the inkjet printing method, the surface of the recording medium is uneven, or the recording medium is large and has distortion or warpage. In this case, there is a concern that the inkjet head and the recording medium come into contact with each other.

  As a method for avoiding the contact, there is a method in which the shortest distance between the ink ejection port of the ink ejection nozzle of the inkjet recording apparatus and the recording medium is 1 mm or more. Specifically, the shortest distance is a distance (gap) from a surface (x) having an ink ejection port of an inkjet head to a position (y) where a perpendicular line of the surface (x) intersects with a recording medium. It is preferable to use an inkjet recording apparatus having a configuration in which the distance is preferably 1 mm or more, more preferably 2 mm or more, and further preferably 3 mm or more.

  The distance from the surface (x) to the position (y) where the perpendicular line assumed to the surface (x) and the recording medium intersect with each other, even if the recording medium is large and easily warped, Prevents contact between the surface of the recording medium and the ink ejection port, and effectively prevents damage to the ink ejection port and ink ejection failure due to deterioration of water repellent function that the ink ejection port often has. In addition to the above, even when the distance between the surface of the recording medium and the inkjet head is long, the effect of flight bending when ink ejection is restarted is minimized, and the outer edge of the printed image is clear. In producing a printed matter with less color unevenness, the lower limit of the distance is preferably 3 mm or more, and the upper limit of the distance is preferably 10 mm or less, particularly preferably 5 mm or less.

  The printed matter obtained by the above method, because the outer edge portion of the printed image is clear and has little color unevenness, for example, it is used for packaging materials such as coated cardboard and corrugated board, plastic films and packaging materials using the same. You can

  Hereinafter, the present invention will be described in more detail with reference to Examples.

  (Production Example 1 Production Method of Aqueous Pigment Dispersion (K-1))

  100 g of carbon black # 960 (manufactured by Mitsubishi Chemical Co., Ltd.) and 40 g of styrene-acrylic acid resin X-1 (manufactured by Seikou PMC Co., Ltd.) were charged into an intensive mixer (manufactured by Nippon Eirich Co., Ltd.), and the rotor peripheral speed was 2.9 m / s. , And were mixed at a pan peripheral speed of 1 m / s. Next, 50 g of PG (propylene glycol manufactured by Asahi Glass Co., Ltd.) and 13 g of a 34 mass% potassium hydroxide aqueous solution were added to the intensive mixer, and the mixture was kneaded for 2 hours at the same rotor peripheral speed and pan peripheral speed as described above.

  Next, while continuing the stirring of the intensive mixer, 464 g of ion-exchanged water was gradually added to the intensive mixer to obtain an aqueous pigment dispersion (K-1) having a pigment concentration of 15% by mass.

(Production Examples 2 to 4 Production Method of Aqueous Pigment Dispersion)
The raw materials and blending ratios used were the raw materials and blending ratios shown in Table 1, and the production method was the same as in Production Example 1 to obtain an aqueous pigment dispersion.

In the table, abbreviations are as follows.
PB15: 3: Phthalocyanine pigment Fastgen Blue Pigment (manufactured by DIC: CI Pigment 15: 3)
PR122: Pigment Red 122
PY74: Pigment Yellow 74

(Method of synthesizing binder resin)
(Synthesis example 1)
In a four-necked flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen introducing tube, 16 g of "Newcol 707SF" (manufactured by Nippon Emulsifier Co., Ltd., anionic emulsifier), "Neugen TDS-200D" (Daiichi Kogyo) 6.5 g of nonionic emulsifier manufactured by Pharmaceutical Co., Ltd. and 220 g of ion-exchanged water were charged, and the temperature was raised to 80 ° C. under a nitrogen stream. Next, an aqueous solution prepared by dissolving 0.8 g of ammonium persulfate in 16 g of ion-exchanged water was added to the flask. Next, a mixed solution of 60 g of 2-ethylhexyl acrylate, 100 g of styrene, 27 g of methyl methacrylate, 0.4 g of 3-methacryloxypropyltrimethoxysilane, 3 g of acrylamide and 6 g of methacrylic acid was added dropwise to the flask over 3 hours. After completion of the dropping, the styrene and the like were reacted for 2 hours and then cooled to 25 ° C. Next, 1.5 g of 28 mass% aqueous ammonia was added to the flask. Next, ion-exchanged water was added to the flask to obtain an acrylic resin aqueous dispersion (E-1) having a glass transition temperature (Tg) of 35 ° C. and a volume average particle diameter of 50 nm. The solid content concentration of the acrylic resin dispersion liquid (E-1) was 39% by mass.

(Preparation of water-based ink)
(Preparation Example 1 Method for preparing aqueous ink)
In 21.63 g of the aqueous pigment dispersion (K-1), propylene glycol 19.68 g, glycerin 10.0 g, ethylene urea 5.6 g, triethanolamine 0.2 g, SURFYNOL 104PG50 (EVONIK acetylene glycol-based surfactant) ) 1.1 g, ACTICIDE B-20 (manufactured by Saw Japan Co., preservative) 0.1 g, acrylic resin water dispersion (E-1) 9.9 g obtained in Synthesis Example 1, ion-exchanged water 31 0.79 g was added and stirred to obtain an aqueous ink (J1).

(Preparation Examples 2 to 11 Preparation method of aqueous ink)
Aqueous inks (J2) to (J11) were obtained in the same manner as in Preparation Example 1, except that the composition of the ink was changed as shown in Tables 1 and 2.

(Comparative Preparation Examples 1 to 4 Preparation Method of Aqueous Ink)
Aqueous inks (J'1) to (J'4) were obtained in the same manner as in Preparation Example 1, except that the composition of the ink was changed as shown in Table 3.

  In the table, abbreviations are as follows.

PG: Propylene glycol GLY: Glycerin TEA: Triethanolamine B-20: ACTICIDE B-20 (preservative made by Saw Japan Co., active ingredient 20% by mass)
SF104PG50: SURFYNOL 104PG50 (surfactant manufactured by EVONIK., Active ingredient 50% by mass)
SF420: SURFYNOL 420 (acetylene-based surfactant manufactured by EVONIK. 100% by mass of active ingredient)
SF465: SURFYNOL 465 (acetylene-based surfactant manufactured by EVONIK. Active ingredient 100% by mass)
Dynol 604: (acetylene-based surfactant manufactured by EVONIK. 100% by mass of active ingredient)
Dynol 607: (acetylene surfactant manufactured by EVONIK. Active ingredient 100% by mass)
TEGOWET KL245: (siloxane-based surfactant manufactured by EVONIK. 100% by mass of active ingredient)
TEGOWET 250: (Siloxane-based surfactant manufactured by EVONIK. Active ingredient 100% by mass)
TEGOWET 280: (Siloxane-based surfactant manufactured by EVONIK. 100% by mass of active ingredient)

[Calculation of optical density ratios (D ¹ ) / (D ¹⁰ ) and (D ² ) / (D ¹⁰ )]
The inkjet head KJ4B-YH manufactured by Kyocera Co., Ltd. is filled with the water-based inks obtained in Examples and Comparative Examples, respectively, and the water head difference of the ink sub-tank from the head nozzle plate surface is set to +35 cm and negative pressure -5.0 kPa. The supply pressure was adjusted with. Further, the distance (gap) from the surface (x) having the ink ejection port of the inkjet head to the position (y) where the perpendicular line assumed to the surface (x) intersects with the recording medium is set to 1 mm. . In a 25 ° C. environment, a photographic paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Co., Ltd.) is prepared as a recording medium, and ink is ejected from a plurality of ejection nozzles by using the inkjet printing device (the amount of one drop of ink is 12 pl). Is discharged to perform 100% solid printing in a range of 2 cm in length and 10 cm in width of the recording medium.

  After the completion of the printing, the ink ejection was stopped for 1 minute.

  After being left, the inkjet heads KJ4B-YH provided in the inkjet printing apparatus are ejected on the photo paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Corp.) to create a preset print image (FIG. 1). A printed matter was obtained by ejecting 16 ink droplets (12 pl per droplet) from 89 of the nozzles.

The image of the printed matter was photographed using an optical microscope (manufactured by KEYENCE, magnification: 30 times), and the image was taken into a computer. Next, of the printed matter (FIG. 1), an image printed in a range indicated by 2 in FIG. 2 (consisting of 16 dots formed by 1 to 16 drops of ink ejected from one inkjet head) Image) and using image processing software (Image J), one minute after the ink jet recording apparatus stops ejecting ink, the second ink droplet (X ² ), the color density (D ² ) of the image (Y ² ) (4 in FIG. 2) and the image (Y ¹⁰ ) ( ^{10 in} FIG. 2) formed by the ^tenth ink droplet (X ¹⁰ ). 5) and the color density (D ¹⁰ ) were measured.

Next, a ratio [coloring density (D ² ) / coloring density (D ¹⁰ )] was calculated based on the values of the above-mentioned color density (D ² ) and color density (D ¹⁰ ). In the image processing software (Image J), the image captured by the method was binarized, and then "Light Background" was selected to remove light unevenness and noise in the image. From the processed image, the image (Y ² ) and the image (Y ¹⁰ ) whose color density is to be measured are selected with a linear tool, and by selecting “Plotprofile”, the image (Y ² ) and the image (Y ¹⁰ ) are selected. The gray values of were defined as the color density (D ² ) and the color density (D ¹⁰ ), respectively. Note that among the displayed peaks, the difference between the gray top value having the lowest gray value and 255 is the color density (D ² ) and the color density (D ¹⁰ ), respectively.

Further, the image of the printed matter was photographed using an optical microscope (manufactured by Keyence, magnification: 200 times), and the image was taken into a computer. Next, in the printed matter (FIG. 1), an image printed in a range 2 shown in FIG. 2 (consisting of 16 dots formed by 1 to 16 drops of ink ejected from one inkjet head) Image) and using image processing software (Image J), one minute after the ink jet recording apparatus stops the ink ejection, the first ink droplet (X ¹ ) and the color density (D ¹ ) of the image (Y ¹ ) (3 in FIG. 2) and the image (Y ¹⁰ ) ( ^{10 in} FIG. 2) formed by the ^tenth ink droplet (X ¹⁰ ). 5) and the color density (D ¹⁰ ) were measured.

Next, the ratio [coloring density (D ¹ ) / coloring density (D ¹⁰ )] was calculated based on the values of the above-mentioned color density (D ¹ ) and color density (D ¹⁰ ). In the image processing software (Image J), the image captured by the method was binarized, and then "Light Background" was selected to remove light unevenness and noise in the image. From the processed image, the image (Y ¹ ) and the image (Y ¹⁰ ) whose color density is to be measured are selected with a linear tool, and the “Plotprofile” is selected to select the image (Y ¹ ) and the image (Y ¹⁰ ). The gray values of were defined as the coloring density (D ¹ ) and the coloring density (D ¹⁰ ), respectively. In addition, among the displayed peaks, the difference between the gray top value having the lowest gray value and 255 is defined as the coloring density (D ¹ ) and the coloring density (D ¹⁰ ), respectively.

[Evaluation of Flight Deflection of First and Second Drops of Ink]
The inkjet head KJ4B-YH manufactured by Kyocera Co., Ltd. is filled with the water-based inks obtained in Examples and Comparative Examples, respectively, and the water head difference of the ink sub-tank from the head nozzle plate surface is set to +35 cm and negative pressure -5.0 kPa. The supply pressure was adjusted with. Further, the distance (gap) from the surface (x) having the ink ejection port of the inkjet head to the position (y) where the perpendicular line assumed to the surface (x) intersects with the recording medium is set to 1 mm. . In a 25 ° C. environment, a photographic paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Co., Ltd.) is prepared as a recording medium, and ink is ejected from a plurality of ejection nozzles by using the inkjet printing device (the amount of one drop of ink is 12 pl). Is discharged to perform 100% solid printing in a range of 2 cm in length and 10 cm in width of the recording medium.

  After the completion of the printing, the ink ejection was stopped for 1 minute.

  After being left, the inkjet heads KJ4B-YH provided in the inkjet printing apparatus are ejected on the photo paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Corp.) to create a preset print image (FIG. 1). A printed matter was obtained by ejecting 16 ink droplets (12 pl per droplet) from 89 of the nozzles.

  It is formed by observing the image of the printed matter using an optical microscope (manufactured by KEYENCE, magnification: 30 times), and connecting dots of ink droplets ejected from the respective ejection nozzles to the tenth droplet of the printed matter. When a line (Z10, a line formed by connecting dots existing in a row indicated by 8 in FIG. 3) is used as a reference, a dot formed by the first ink droplet ejected from each ejection nozzle Whether the line formed by connecting (Z1, the line formed by connecting the dots existing in the row indicated by 6 in FIG. 3) is a straight line or a curved line (in other words, the dots are linear) It was evaluated whether or not they were lined up.

  Further, when the line (Z10) is used as a reference, a line (Z2, a line indicated by 7 in FIG. 3) formed by connecting dots formed by the second ink droplets ejected from each ejection nozzle. It was evaluated whether or not the line formed by connecting the dots existing in 1) is bent (in other words, whether or not the dots are linearly arranged).

  Further, it was evaluated whether or not the intervals between the line (Z1) and the line (Z2) were equal.

Based on the above evaluation results, the presence or absence of flight bending of the first and second drops of ink was evaluated according to the following evaluation criteria.
A Since both the line (Z1) and the line (Z2) are straight lines having the same degree as the reference (line (Z10)), the intervals between the line (Z1) and the line (Z2) are also equal. It was evaluated that flight bending of the first and second ink droplets did not occur.
B Although both the line (Z1) and the line (Z2) were straight lines similar to the reference (line (Z10)), the line (Z1) and the line (Z2) were clearly wide. Since a narrow portion was confirmed, it was evaluated that the flight bending of the first and second ink droplets slightly occurred.
C Both the line (Z1) and the line (Z2) are not straight lines of the same degree as the reference (line (Z10)) but are both distorted lines, and the distance between the line (Z1) and the line (Z2) It was evaluated that the flight bending of the first and second ink droplets was remarkably generated, since a wide area and a narrow area were confirmed.

[Sharpness of printed edge]
The inkjet head KJ4B-YH manufactured by Kyocera Co., Ltd. is filled with the water-based inks obtained in Examples and Comparative Examples, respectively, and the water head difference of the ink sub-tank from the head nozzle plate surface is set to +35 cm and negative pressure -5.0 kPa. The supply pressure was adjusted with. Further, the distance (gap) from the surface (x) having the ink ejection port of the inkjet head to the position (y) where the perpendicular line assumed to the surface (x) intersects with the recording medium is set to 1 mm. . In a 25 ° C. environment, a photo paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Corporation) is prepared as a recording medium, and the recording medium is recorded using an inkjet printing device (adjusting the amount of one drop of ink to 12 pl). 100% solid printing was performed in a range of 2 cm in length and 10 cm in width.

  After the completion of the printing, the ejection of ink was stopped, and then the ink was left for 1 minute. After the lapse of 1 minute, 100% solid printing similar to the above was again performed on the photographic paper Crispia high gloss (KA420SCKR manufactured by Seiko Epson Corporation), and its edge (vertical 2 cm edge) was visually observed. The following criteria were used for evaluation.

(Evaluation criteria)
A: There was no blur or unevenness on the edge, and the edge was on a straight line.

  B: The above-mentioned end had some blur, but there were few irregularities, and the end was slightly distorted.

  C: The edges were markedly scratched and uneven, and the edges were greatly distorted.

From the evaluation results of Table 1 and Table 2, in Examples 1 to 11 using the ink according to the present embodiment, the optical density ratio (D ¹ ) / (D ¹⁰ ) was in the range of 0.4 to 1.5. And (D ² ) / (D ¹⁰ ) is in the range of 0.75 to 1.5, and there is no printing defect such as lightening of the color at the printed edge, and the edge becomes clear. I understand. However, as in Example 10, for example, the optical density ratio (D ¹ ) / (D ¹⁰ ) is in the range of 0.4 to 1.5, and (D ² ) / (D ¹⁰ ) is 0. Even in the range of 75 to 1.5, when the ejection deviation of the first drop is large, the sharpness of the printed end portion is slightly reduced.

[Wettability]
A contact angle meter (Kyowa Interface Science Co., Ltd., product name "DropMaster DMo-501") was used to measure the dynamic contact angle of the ink droplet by a liquid suitability method (change with time). Specifically, when 1 μL of each ink is dropped onto “OK Top Coat +” (basis weight of 157 g / m ² ) manufactured by Oji Paper Co., Ltd., and when the ink drops come into contact with the “OK Top Coat +”. After 1000 milliseconds, the contact angle was measured using the contact angle meter.

(Evaluation criteria)
A: The contact angle was less than 20 °, and the wetting and spreading on the surface of “OK top coat +” was good.

  B: The contact angle was 20 ° or more and 22 ° or less, and the wetting and spreading on the surface of “OK top coat +” was generally good.

  C: The contact angle was higher than 22 °, and the wetting and spreading on the surface of "OK top coat +" was poor.

[Storage stability]
Each ink was allowed to stand in a constant temperature bath at 60 ° C. for 4 weeks, and the rate of change in viscosity and surface tension of the ink before and after being allowed to stand in the constant temperature bath were measured and evaluated according to the following criteria. The rate of change in viscosity refers to a value calculated by [(viscosity of ink before standing-viscosity of ink after standing) / (viscosity of ink before standing)] × 100, The rate of change of the surface tension is a value calculated by [(surface tension of ink before standing-surface tension of ink after standing) / (surface tension of ink before standing)] × 100 Point to.

The viscosity of the ink was measured under the following conditions using a cone-plate (cone-plate) rotational viscometer corresponding to an E-type viscometer.
Measuring device: TVE-25 type viscometer (manufactured by TVE-25L)
Calibration standard solution: JS20
Measurement temperature: 32 ° C
Rotation speed: 10-100 rpm
Injection volume: 1200 μL
The surface tension of the ink means a value measured under the following conditions using an automatic surface tension meter to which the Wilhelmi method is applied. According to the Wilhelmy method, the static surface tension and the dynamic surface tension can be measured, but the surface tension of the ink in the present invention represents the value of the static surface tension.
Measuring device: Automatic surface tensiometer (Kyowa Interface Science Co., Ltd., CBVP-Z type)
Measurement temperature: 25 ° C
Stylus: Platinum plate (evaluation standard)
A: Change rate of viscosity and surface tension is less than ± 5% B: Change rate of viscosity and surface tension is ± 5% or more, less than 10% C: Change rate of viscosity and surface tension is ± 10% or more

1: Printed image 1 used for ink evaluation, etc.
2: A part 2 of the print image used to calculate the ratio [color density (D ² ) / color density (D ¹⁰ )] of the print image 1
3: Image 3 consisting of dots formed by the first ink droplet ejected from one ejection nozzle 3
4: Image 4 composed of dots formed by the second ink droplet ejected from one ejection nozzle
5: Image 5 consisting of dots formed by the 10th ink droplet ejected from one ejection nozzle 5
6: Row 6 consisting of dots formed by the first ink droplet ejected from 89 ejection nozzles
7: Row 7 consisting of dots formed by the second ink droplet ejected from 89 ejection nozzles
8: Row 8 consisting of dots formed by the ink droplet ejected from the 89th ejection nozzle to the 10th droplet

Claims (13)

In the process of manufacturing a printed matter using the inkjet recording apparatus, one minute after the inkjet recording apparatus stops ejecting ink, the second ink droplet (X ² ) when ejecting the ink again is photographic paper crispia. The color density (D ² ) of the image (Y ² ) formed by landing on the high gloss (Seiko Epson KA420SCKR) and the tenth ink droplet (X ¹⁰ ) are photographic paper Crispia high gloss (Seiko Epson) Ltd., ratio of the color density ^{(D 10)} for landed the image formed in KA420SCKR) ^{(Y 10)} [color density ^(D 2) / color density ^{(D 10)]} is 0.75 to 1.5 A pigment ink for inkjet recording, wherein In the process of manufacturing a printed matter using an inkjet recording apparatus, one minute after the inkjet recording apparatus stops ejecting ink, the first ink droplet (X ¹ ) when ejecting the ink again is photographic paper crispia. The color density (D ¹ ) of the image (Y ¹ ) formed by landing on the high gloss (Seiko Epson KA420SCKR) and the 10th ink drop (X ¹⁰ ) are photographic paper Crispia high gloss (Seiko Epson) Ltd., ratio of the color density ^{(D 10)} for landed the image formed in KA420SCKR) ^{(Y 10)} [color density ^(D 1) / color density ^{(D 10)]} is 0.4 to 1.5 The pigment ink for inkjet recording according to claim 1, which is The pigment ink for inkjet recording according to claim 1, which contains a pigment, a surfactant and an aqueous medium. The inkjet recording pigment ink according to any one of claims 1 to 3, wherein the surfactant contains an acetylene-based surfactant (A) having 10 or more carbon atoms in a main chain. The pigment ink for inkjet recording according to claim 4, wherein the acetylene-based surfactant (A) has a polyoxyethylene structure. The pigment ink for inkjet recording according to claim 4 or 5, wherein the acetylene-based surfactant (A) is contained in an amount of 0.1 to 5 mass% with respect to the total amount of the inkjet recording ink. The pigment ink for inkjet recording according to any one of claims 2 to 6, further comprising a pigment dispersion resin, a binder resin and a compound having a urea bond. A printed matter, wherein the pigment contained in the inkjet recording pigment ink according to any one of claims 1 to 7 is present on the surface of a recording medium. A method for producing a printed matter, which comprises a step [1] of ejecting the inkjet recording pigment ink according to any one of claims 1 to 7 onto a recording medium using an inkjet recording apparatus. After 1 minute from the time when the ink ejection was stopped, the second ink droplet (X ² ) when the ink was ejected again landed on the recording medium and the coloring density (( ² ) of the image (Y ² ) formed. D ² ) and the color density (D ¹⁰ ) of the image (Y ¹⁰ ) formed by the ^10th ink droplet (X ¹⁰ ) landing on the recording medium [color density (D ² ) / color density] Density (D ¹⁰ )] is 0.75 to 1.5. One minute after the inkjet recording apparatus ejects the ink again, the first ink droplet (X ¹ ) lands on the recording medium 1 minute after the inkjet recording apparatus stops ejecting the ink. color density of the formed image ^{(Y 1)} and ^{(D 1),} wherein 10 drop at the ink droplet ^{(X 10)} the color density of the recording medium to land on the imaged ^{(Y 10) (D 10)} The method for producing a printed matter according to claim 9, wherein the ratio [coloring density (D ¹ ) / coloring density (D ¹⁰ )] is 0.4 to 1.5. The method for producing a printed matter according to claim 9, wherein the shortest distance between the ink ejection port of the ink ejection nozzle of the inkjet recording device and the recording medium is 1 mm or more. 12. The recording medium has a water absorption amount of 10 g / m ² or less when the contact time between the recording surface of the recording medium and water is 100 msec. 12. The method for producing a printed matter according to. The method for producing a printed matter according to any one of claims 9 to 12, wherein the inkjet recording apparatus has an ink ejection line head and is an apparatus capable of printing a sheet of recording medium.

Images