JP2007145926A - Ink set for inkjet and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set which is used for inkjet, prevents curling, when recording on plain paper, and gives high image density in color-mixed portions, preferably when printed with a line printer, and has high good print-through resistance, and to provide an inkjet recording method. <P>SOLUTION: This ink set used for inkjet and comprising two or more color ink each comprising at least a colorant, organic solvents, and water is characterized in that the water content is 10 to 50 mass% based on the total ink mass; at least one of the organic solvents is a water-soluble organic solvent having an SP value of 16.5 to 24.6; the content of the water-soluble organic solvent having an SP value of 16.5 to 24.6 is ≥30 mass% based on the total mass of the ink; and the more early the order of printing is, the higher the density of the colorant in the ink is. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet ink set comprising a novel ink and an ink jet recording method using the ink set.

  In recent years, the inkjet recording method can create images easily and inexpensively, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, ink jet recording devices that emit and control fine dots, ink with improved color reproduction range, durability, and emission suitability, ink absorbency, colorant color development, surface gloss, etc. are dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper.

  However, in an inkjet image recording system that requires dedicated paper, there are problems in that the recording media that can be used are limited and the cost of the recording media is increased.

  On the other hand, in the office, there is an increasing need for a system that can perform full-color printing at high speed without being restricted by recording media (for example, plain paper, coated paper, art paper, double-sided printing on plain paper, etc.). Further, it is being applied to so-called POD printing taking advantage of the fact that no printing plate is required. In such a business field, it is essential to improve the printing speed because the number of copies to be printed is larger than that in the home or office, and the printer also scans by moving the conventional inkjet head in the direction intersecting the recording material conveyance direction. Instead of the serial printing method, a line printing method using a line head in which an inkjet head is fixedly arranged in a direction intersecting with the conveyance direction of the recording material is used.

  As for the composition of the ink-jet ink, it can be printed at high speed, has good character reproducibility on plain paper, and shows through when printing (a phenomenon in which the printed ink passes through the recording medium and the image is reflected on the back). Various studies have been made so far from the viewpoints of no occurrence, rapid penetration into paper, and quick drying. In particular, it is necessary to satisfy all these characteristics in plain paper high-speed duplex printing.

  However, so-called water-based inks, which are generally used as inkjet inks and contain water as a main component, tend to cause curling on plain paper. This is considered to occur because hydrogen bonds between cellulose fibers of the paper deviate from the original position after swelling, and various improvements have been studied, but it is still insufficient (see, for example, Patent Document 1).

  In contrast, non-aqueous inks are less affected by cellulose hydrogen bonds and are less likely to curl, and line printers that use non-aqueous inks are also commercially available, but non-aqueous inks have large show-through. (For example, Patent Document 2).

On the other hand, the present inventor has found an ink that can simultaneously prevent both curling and back-through, and has made some disclosures regarding these techniques (Patent Documents 3 to 6). However, it has been found that in a line printer that prints at high speed, even when the same ink set is used, the image density of the mixed color portion is lower than that of a serial printer, and it is easy to see through.
JP 2004-217930 A JP 2005-193660 A JP 2004-29014 A JP 2004-31738 A JP 2004-31739 A JP 2004-31740 A

  An object of the present invention is to provide an ink jet ink set and an ink jet recording method that prevent curling in plain paper recording, and that have high image density in a mixed color portion in a line printer and good anti-through-through characteristics. It is.

  The object of the present invention can be achieved by the following constitution.

  1. An ink-jet ink set comprising at least two colors of ink containing a colorant, an organic solvent, and water, wherein the water content in each ink in the ink-jet ink set is 10 mass relative to the total ink mass % Or more and less than 50% by mass, and at least one organic solvent is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and the SP value is 16.5 or more, Ink-jet ink set characterized in that the content of the water-soluble organic solvent of less than 24.6 is 30% by mass or more of the total ink mass, and the earlier the printing order, the higher the colorant concentration in the ink. .

  2. An ink jet recording method for printing using an ink set for ink jet comprising at least a color material, an organic solvent, and water containing two or more colors, wherein the water content in each ink in the ink jet ink set is: , And at least one organic solvent is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, The content of the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 30% by mass or more of the total ink mass, and the color material concentration in the ink is high in the ink set. An ink jet recording method characterized in that the printing order is earlier.

  3. 3. The ink jet recording method according to 2 above, wherein the head used for printing is a line head.

  4). 4. The ink jet recording method according to 3 above, wherein the line head has a resolution of 360 dpi or more and a drive frequency of 7 kHz or more.

  According to the present invention, it is possible to obtain an ink jet ink set and an ink jet recording method that prevent curling, particularly in plain paper recording with a line printer, and that have a high image density in a mixed color portion and good anti-through-through characteristics during printing.

  Hereinafter, the best mode for carrying out the present invention will be described, but the present invention is not limited thereto.

  First, an ink according to the present invention containing a pigment, an organic solvent, and water, and an ink set for ink jet will be described.

  The present inventor has considered the reason why the image density of the color mixture portion tends to be lower in the line printer than in the serial printer. In the serial printing method, since the printing area is filled by a plurality of operations, the solvent in the ink is easily dried before the adjacent dots are printed. In contrast, the line printing method prints all dots in one pass. Normally, the line heads are printed separately for each color. However, it is desirable that the distance between the line heads is narrow for compactness of the apparatus, and further, the time interval for printing different color inks is used for high-speed printing. Since a shorter one is desirable, when the next ink is printed at a stage where the solvent is less dried, the density of the color material (for example, pigment) of the printed ink in the paper is lower, but The color material (pigment) tends to be difficult to adhere to the paper surface when the ink concentration is low. This is considered to be because, for example, aggregation of the pigment to the cellulose fiber is likely to occur when the pigment concentration is high, but conversely, aggregation is difficult to occur when the pigment concentration is low.

  Thus, as a result of intensive studies, the present inventor has found that the image density in the mixed color portion is increased and the show-through is reduced by performing printing in order from the ink having the highest pigment concentration. As described above, for example, when ink with a high pigment concentration is printed first, the pigment aggregates on the paper surface, and when this is fixed a lot, the pigment of the next printed ink has already aggregated. This is considered to be because it tends to be compatible with the pigment and is easily fixed to the paper surface.

  The present invention is most desirably all of the combinations of ink sets, but the effect is exhibited even in a partial order.

  In the present invention, the head used for printing is preferably a line head.

  In particular, the present invention makes it easy to fix the pigment in the ink to the paper surface when high-speed printing is required, that is, when the line head requires a resolution of 360 dpi or higher, a driving frequency of 7 kHz or higher, or higher. Can exert its effect. In the present invention, dpi represents resolution, specifically, the number of dots per 2.54 cm.

"solvent"
The solvent composition in the ink of the present invention contains at least water and an organic solvent, the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and at least one of the organic solvents is SP. A water-soluble organic solvent having a value of 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 30% by mass or more of the total ink mass. By using this solvent composition, the emission stability and decap resistance are excellent, the character quality of the formed image and the through-through resistance are good, and the curled characteristics of the printed recording material are good. It becomes possible.

  If the water content in the total ink mass is less than 50 mass%, the occurrence of curling and cockling is suppressed. Moreover, if it is 10 mass% or more, favorable dispersion stability of the pigment can be obtained. The water content in the total ink mass is preferably 20% by mass or more and less than 40% by mass.

  The ink of the present invention contains a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 at least 30% by mass of the total ink mass. The occurrence of cockling can be drastically suppressed. Preferably, the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is contained in an amount of 50% by mass to 80% by mass based on the total ink mass. It is preferable.

  In the ink of the present invention, the SP value of the main organic solvent is 16.5 or more and less than 24.6, but if it is 16.5 or more, the compatibility with water becomes good and the separation from water is improved. It does not occur and high dispersion stability of the pigment particles can be maintained. Moreover, if SP value is less than 24, 6, the inhibitory effect with respect to the curl resulting from an organic solvent can be acquired. In the present invention, the range of the SP value of the organic solvent is more preferably 16.5 or more and less than 22.5.

SP value in the present invention The SP value of the solvent is a solubility parameter (SP value), and the solubility parameter (SP value) is a value represented by the square root of the molecular agglomeration energy. Polymer HandBook (Second Edition) IV There is a description in Chapter Solubility Parameter Values, and the value was used. The unit is (MPa) ^1/2 and refers to the value at 25 ° C. In addition, R.D. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1967). Hereinafter, some examples of water-soluble organic solvents having an SP value of 16.5 or more and less than 24.6 are shown together with the SP value (the value in () is SP value). Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (24.5)
Ethylene glycol monoethyl ether (23.5)
Ethylene glycol monobutyl ether (22.1)
Ethylene glycol monoisopropyl ether (22.3)
Diethylene glycol monomethyl ether (23.0)
Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Diethylene glycol diethyl ether (16.8)
Triethylene glycol monomethyl ether (22.1)
Triethylene glycol monoethyl ether (21.7)
Triethylene glycol monobutyl ether (21.1)
Propylene glycol monomethyl ether (23.0)
Propylene glycol monophenyl ether (24.2)
Dipropylene glycol monomethyl ether (21.3)
Tripropylene glycol monomethyl ether (20.4)
1,3-dimethyl-2-imidazolidinone (21.8)
In the ink of the present invention, in addition to a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, various conventionally known water-soluble organic solvents can be used in combination. Among these, ethylene carbonate, propylene carbonate, 1,3-dimethyl-2-imidazolidinone is preferable because it does not adversely affect the dispersibility of the pigment and has an effect of lowering the ink viscosity.

《Coloring material》
The ink of the present invention contains a color material, and examples of the color material used in the ink of the present invention include a color material that forms yellow, magenta, cyan, black, blue, green, and red inks. Are preferably used, and particularly preferable are yellow, magenta, cyan, and black color materials.

  In the ink of the present invention, a dye ink whose color material is a dye, or a pigment ink that forms a dispersion containing fine pigment particles, or a color material that is insoluble in a solvent constituting the ink-jet ink, The present invention can be applied to various ink-jet inks such as a dispersion ink composed of a molecular polymer dispersion.

  Examples of the dye that can be used in the present invention include azo dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, diphenylmethane dyes, and the specific compounds include: For example, the dye illustrated in Unexamined-Japanese-Patent No. 2002-264490 can be mentioned.

  In addition, oil-soluble dyes that form colored fine particles together with polymers, etc., and become colorants, are usually soluble in organic solvents that do not have a water-soluble group such as carboxylic acid and sulfonic acid, and are insoluble in water, such as disperse dyes. Etc. are selected. Also included are dyes that exhibit oil solubility by salting a water-soluble dye with a long-chain base. For example, acid dyes, direct dyes, salt-forming dyes of reactive dyes and long-chain amines are known. .

  However, in the ink of the present invention, it is preferable to use a pigment as the coloring material, and a pigment that does not have solubility in the solvent composition according to the present invention is preferable from the viewpoint of exerting the intended effects of the present invention.

  As the pigment that can be used in the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments, and the like can be used, for example, organic pigments such as insoluble pigments and lake pigments, An inorganic pigment such as carbon black can be preferably used. The pigment is present in a dispersed state in the water-based ink. The dispersion method may be any of self-dispersion, activator dispersion, polymer dispersion, and microcapsule dispersion, but the polymer dispersion and microcapsule dispersion are fixed. From the viewpoint of sex.

  The insoluble pigment is not particularly limited. Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the pigment for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  In addition to the above pigments, when red, green, blue and intermediate colors are required, the following pigments are preferably used alone or in combination. I. Pigment Red; 209, 224, 177, 194, C.I. I. Pigment Orange; 43, C.I. I. Vat Violet; 3, C.I. I. Pigment Violet; 19, 23, 37, C.I. I. Pigment Green; 36, 7, C.I. I. Pigment Blue; 15: 6 or the like is used.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle size of the pigment dispersion used in the ink of the present invention is preferably 50 nm or more and less than 200 nm. When the average particle size of the pigment dispersion is less than 50 nm or 200 nm or more, the stability of the pigment dispersion tends to deteriorate, and the storage stability of the ink tends to deteriorate.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate and often used.

  The pigment used in the present invention is preferably used after being dispersed by a disperser together with a dispersant and other necessary additives according to desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. Among them, the dispersion by sand mill is preferable because the particle size distribution is sharp when the dispersion is aimed at an average particle diameter of around 100 nm. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Further, the bead diameter is preferably 0.1 mm or more and 0.5 mm.

<Pigment dispersant>
Examples of the polymer dispersant for dispersing the pigment according to the present invention include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, polyphosphates, and the like. Activators such as oxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide, or styrene, styrene derivatives, vinyl A block copolymer comprising at least two monomers selected from naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, and randoma Copolymer and can be exemplified salts thereof.

  In the present invention, the addition amount of the pigment dispersant is preferably 10 to 100% by mass with respect to the pigment in the ink.

<Surfactant>
In the dispersion of the pigment according to the present invention, a surfactant can be used as an additive. As the surfactant used in the present invention, any of cationic, anionic, amphoteric and nonionic surfactants can be used, but it is particularly preferable to use a nonionic surfactant from the viewpoint of dispersion stability.

  Nonionic activators include, for example, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester , Polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, poly Oxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide , Acetylene glycol, acetylene alcohol, and the like.

  Further, it is preferable to use a surfactant in order to accelerate the penetration of ink droplets after ink ejection into plain paper, and such a surfactant has an adverse effect on the ink, such as storage stability. The surfactant is not limited as long as it does not affect the surface, and the same surfactants as those used as an additive at the time of dispersion can be used.

《Polyvalent metal ion》
In the ink of the present invention, the total content of calcium ions, magnesium ions and iron ions, which are polyvalent metal ions, is preferably 10 ppm or less, more preferably 0.1 to 5 ppm, particularly preferably. 0.1-1 ppm.

  By setting the content of polyvalent metal ions in the inkjet ink to the amount specified above, an ink having high dispersion stability can be obtained. The polyvalent metal ions according to the present invention are contained in sulfates, chlorides, nitrates, acetates, organic ammonium salts, EDTA complex salts and the like.

《Other additives》
In the ink of the present invention, in addition to the above description, if necessary, the output stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performance improvement objectives are known. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust preventives, etc. may be appropriately selected and used. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, ultraviolet absorbers described in JP-A-57-74193, 57-87988, and 62-261476, As described in Kaisho 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Anti-fading agents, fluorescent whitening agents described in JP-A Nos. 59-42993, 59-52689, 62-280069, 61-242871, and JP-A-4-219266 Can be mentioned.

  In addition, the dissolved oxygen concentration in the ink of the present invention is preferably 2 ppm or less at 25 ° C. By setting this dissolved oxygen concentration condition, the formation of bubbles can be suppressed, and the emission stability even in high-speed printing. An ink jet recording method having excellent properties can be realized. As a method for measuring the dissolved oxygen dissolved in the ink, for example, it can be measured using a dissolved oxygen measuring device DO-14P (manufactured by Toa Radio).

"Recording method"
In the image recording method using the ink of the present invention, for example, an ink jet print can be obtained by ejecting ink as droplets from an ink jet head based on a digital signal and adhering it to plain paper by a printer loaded with ink jet ink. .

  When an image is formed by ejecting the ink of the present invention, the inkjet head to be used may be an on-demand system or a continuous system. Also, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, thermal ink jet) Any ejection method such as a mold, a bubble jet (registered trademark) mold, or the like may be used.

  Among them, in the ink jet recording method according to the present invention, the ink of the present invention is ejected from a piezo ink jet recording head having a nozzle diameter of 30 μm or less to perform recording on plain paper, and further, the nozzle diameter is 30 μm or less. It is preferable to perform recording on plain paper by discharging from a piezo-type ink jet recording head having a line head.

  As a printing method of an ink jet printer, the printing characteristics of the ink of the present invention can be sufficiently obtained by printing using a line head type recording head with respect to a shuttle head type recording head. It is possible to achieve a very good dot shape (roundness) and printing accuracy when droplets land on plain paper.

  In particular, it is preferable to apply the ink of the present invention to an ink jet recording system in which images are printed on both sides of plain paper from the viewpoint that the object and effects of the present invention can be exhibited.

  In double-sided printing, after printing on one side, plain paper is turned over and transported with the printing side down, but the ink of the present invention has the above-mentioned characteristics. Since there is no bleeding of characters, high density and excellent character quality on any surface, no conveyance failure occurs, and the conveyance belt is not contaminated with ink.

"recoding media"
The plain paper used in the ink jet recording method using the ink of the present invention is not particularly limited, but non-coated paper, special printing paper, and 80 to 200 μm uncoated paper belonging to a part of information paper are desirable. The construction of the plain paper according to the present invention is made by a conventional method using mainly chemical pulps represented by LBKP and NBKP, sizing agents and fillers, and using other paper making aids as necessary. As the pulp material used for the plain paper according to the present invention, mechanical pulp and recycled paper recycled pulp may be used in combination, and there is no problem even if these are used as the main material.

  Examples of the sizing agent internally added to the plain paper according to the present invention include rosin size, AKD, Alnicel succinic anhydride, petroleum resin-based size, epichlorohydrin, cationic starch, and acrylamide.

  Examples of the filler internally added to the plain paper according to the present invention include finely divided silicic acid, aluminum silicate, diatomaceous earth, kaolin, kaolinite, halloysite, nacrite, dickite, pyrophyllite, sericite, titanium dioxide, bentonite and the like. Is mentioned.

  Further, the plain paper according to the present invention may contain a water-soluble polyvalent metal salt from the viewpoint of enhancing the strike through of the ink of the present invention and the fixability of the pigment. The water-soluble polyvalent metal salt is not particularly limited, but for example, aluminum, calcium, magnesium, zinc, iron, strontium, barium, nickel, copper, scandium, gallium, indium, titanium, zirconium, tin, lead, etc. It is added as a salt such as a metal salt, sulfate, nitrate, formate, succinate, malonate, chloroacetate or p-toluenesulfonate. Further, a water-soluble inorganic polymer such as polyaluminum chloride may be used as a salt of a water-soluble polyvalent metal ion. The water solubility is preferably at least 0.1% by mass, more preferably 1% by mass. Among these, a water-soluble salt composed of aluminum, calcium, aluminum, magnesium, and zinc is preferable because its metal ion is colorless. Particularly preferred are aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum acetate, calcium chloride, calcium sulfate, calcium nitrate, calcium acetate, magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium acetate, zinc chloride, zinc sulfate, zinc nitrate, Zinc acetate. In the present invention, in addition to plain paper, high-quality paper, art paper, coated paper, cast-coated paper, glossy paper, ink jet paper, and the like can be widely used.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<Preparation of ink>
(Preparation of pigment dispersion)
(Preparation of yellow pigment dispersion)
The following additives are mixed, put together with 200 g of zirconia beads having a diameter of 0.5 mm in a polypropylene plastic bottle, sealed, and dispersed for 5 hours using a paint shaker. The magenta pigment content is 15%. A dispersion was prepared.

C. I. Pigment Yellow 138 15 parts Joncrill 501 (manufactured by Johnson Polymer) (solid content 30% aqueous solution) 20 parts Tripropylene glycol monomethyl ether 56 parts Water 19 parts (Preparation of magenta pigment dispersion, cyan pigment dispersion, and black pigment dispersion) )
In the preparation of the yellow pigment dispersion, C.I. I. Instead of CI Pigment Yellow 150, C.I. I. Pigment red 122 (magenta pigment dispersion), C.I. I. Pigment blue 15: 3 (cyan pigment dispersion), C.I. I. A yellow pigment dispersion, a magenta pigment dispersion, a cyan pigment dispersion, and a black pigment dispersion were prepared in the same manner except that each was changed to CI Pigment Black 7 (black pigment dispersion).

[Preparation of ink sets A to C]
Using each of the yellow, magenta, cyan and black pigment dispersions prepared above, tripropylene glycol monomethyl ether and water were added to each pigment dispersion so that tripropylene glycol monomethyl ether / water = 7/3. In addition, the pigment concentration in the ink was added to each of the yellow (Y), magenta (M), and cyan (C) concentrations as shown below, and the mixture was sufficiently stirred and then mixed. The mixture was filtered through a # 3500 mesh metal filter, deaerated with a hollow fiber membrane, and A, B, C3 types of ink sets consisting of four colors Y, M, C, and K (black) were produced.

Ink set A; Y (5.0%), M (4.5%), C (4.0%), K (5.5%)
Ink set B; Y (4.5%), M (5.0%), C (4.0%), K (5.5%)
Ink set C; Y (4.0%), M (4.5%), C (5.0%), K (5.5%)
Moreover, the following ink set was produced.

[Preparation of ink set b]
As a solvent for each color pigment dispersion of ink set A, Y was added in the same manner as ink set A except that 75 parts of tripropylene glycol monomethyl ether was dispersed without using water and only tripropylene glycol monomethyl ether was added. Yellow), M (magenta), C (cyan), and K (black) inks were prepared.

[Preparation of ink set c]
Y (yellow), M (magenta), C (cyan), C, and cyan, except that a solvent was added to the pigment dispersion so that tripropylene glycol monomethyl ether / water in the ink was 2/8. A K (black) ink was prepared.

[Preparation of ink set d]
Y (yellow), M (magenta), C (cyan), K (same as ink set A, except that tripropylene glycol monomethyl ether in the pigment dispersion and ink was changed to diethylene glycol (SP value 30.6). Black) ink was prepared.

<< Preparation of image recording sample >>
Each of the ink sets A to C was used for testing as follows.

[Printing by line head]
Piezo-type head (manufactured by Konica Minolta Inkjet Co., Ltd.) with 512 nozzles per head, resolution of 360 dpi, droplet volume of 14 pl, and drive frequency of 12.8 kHz so that the nozzles are arranged at right angles on the belt conveyor. Are arranged in series so that the nozzle row is in the width direction of the recording paper in the transport direction and the nozzles of adjacent heads are 20 mm apart from each other in plain paper; Konica First Class (Konica Minolta Business Technologies) (Made by Co., Ltd.) was placed on a belt conveyor and conveyed at a speed of 350 mm / sec, and printing was performed with four heads.

[Printing by shuttle head]
Also, using the same ink set, align the nozzle row in the recording paper transport direction with a piezo head (Konica Minolta IJ) with 512 nozzles per head, resolution of 360 dpi, droplet volume of 14 pl, and drive frequency of 12.8 kHz. The four color shuttle heads were arranged in parallel so as to be orthogonal to the recording paper conveyance direction (in the main scanning direction), and A4 was printed on plain paper at a printing speed of 15 seconds.

  Evaluation was performed as follows.

(Evaluation of image density)
Color patches are printed on the plain paper (Konica first class) using the ink set A, B, and C, and the inks of Y, M, and C using the line heads in the order shown in Table 1. Was made. Next, the same color patch was printed with the same three colors with the shuttle head, and the reflection densities when the line head and the shuttle head were printed were compared. The patch includes Y, M, and C single colors and Y and M mixed colors R (red), M and C mixed colors B (blue), C and Y mixed colors G (green) and black (K) It is a thing. For each ink set, the printing order was changed as shown in Table 1, and printing was performed. Table 1 shows whether the density was lowered by printing with the line head compared to printing with the shuttle head.

  Also, using the ink sets A to C, using the four color inks obtained by adding K to the Y, M, and C colors, respectively, the color patches are printed by the line head and shuttle head in the same manner as described above. Table 2 shows the results obtained by similarly testing and evaluating whether or not the density of the black patch was reduced by printing with the line head compared to printing with the shuttle head.

[Evaluation of through-hole resistance]
Using the inks A to B on the plain paper (Konica first class), printing was performed using a line head, and the back side of the solid print sample of each color was visually observed, and evaluation of see-through resistance was performed according to the following criteria. It was.

A: No ink bleed or show-through on the back side B: No ink bleed or show-through on the back side is acceptable and acceptable quality C: No ink bleed or show-through on the back side Slightly recognized, but not of concern when printing on the back side D: Ink bleed and back-through on the back side are quite acceptable and unacceptable quality for back-side printing E: Clear ink bleed or back-through on the back side Is not suitable for backside printing [Evaluation of curling resistance]
In each test using a line head on the above plain paper (Konica first class), each color was printed on a solid print with an area of 10 cm × 10 cm, and the sample was left in the environment for one day to measure the curl. The curl when each image was output was evaluated according to the following criteria.

A: No curl B: Slightly curled C: Some expansion and contraction is observed, weak curl is generated but is not a quality that is a problem in practical use D: Large shrinkage, obvious curl generated E: Quality that poses practical problems E: Large shrinkage, strong curl, quality that poses practical problems [Evaluation of intermittent emission suitability]
The pigment ink prepared above was allowed to stand for 10 hours in an environment of 23 ° C. and 20% RH with the ink set loaded in the recording head. Next, after leaving for 10 hours, the ink was ejected under the above conditions, the flying state of the ink droplet was observed, and the intermittent ejection suitability was evaluated according to the following criteria.

A: All the 512 nozzles were emitted when exiting without performing anything after being left. B: When the light was ejected without performing any action after leaving, a flying bend occurred with 1 to 5 nozzles. The normal radiating state was recovered by wiping operation. C: When the light was emitted without any action after being left standing, a flying bend occurred at 1 to 5 nozzles. D: The exit state was recovered. D: When exiting without taking any action after leaving, flying bends occurred at 6 nozzles or more, but the normal exit state was recovered by two suction and wiping operations of the recording head. E: After exiting, when exiting without doing anything, flying bends occurred at 6 nozzles or more, and it was not possible to recover the normal exiting state even with the suction and wiping operations of the recording head twice. , Varying the pigment concentration and C, shows the evaluation results when the changed each print order (test 12).

  Table 2 shows the evaluation results when the printing order of Y, M, and C of the ink set in which the pigment concentrations of Y, M, C, and K were changed (Tests 13 to 18).

  In the case of an ink set printed from an ink having a high pigment concentration, there was no decrease in density, and the back-through resistance, curl resistance, and intermittent emission suitability were good evaluations. Even black, which has the highest density, has a density drop if the printing order is slow.

  Next, printing is performed in the same printing order as in Test 1, using the same line head as in Example 1 using ink sets b, c, and d in which the solvent composition of ink set A and Y, M, and C is changed. Tests were conducted, and the back-through resistance, curl resistance, and intermittent emission suitability were evaluated in the same manner. The evaluation results are shown in Table 3.

  It can be seen that inks having a water-soluble organic solvent content within the range of the present invention and those having the SP value of the water-soluble organic solvent used in the ink within the range of the present invention show good results in all properties.

Claims (4)

An ink-jet ink set comprising at least two colors of ink containing a colorant, an organic solvent, and water, wherein the water content in each ink in the ink-jet ink set is 10 mass relative to the total ink mass % Or more and less than 50% by mass, and at least one organic solvent is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and the SP value is 16.5 or more, Ink-jet ink set characterized in that the content of the water-soluble organic solvent of less than 24.6 is 30% by mass or more of the total ink mass, and the earlier the printing order, the higher the colorant concentration in the ink. . An ink jet recording method for printing using an ink set for ink jet comprising at least a color material, an organic solvent, and water containing at least two inks, wherein the water content in each ink in the ink jet ink set is: , And at least one organic solvent is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, The content of the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 30% by mass or more of the total ink mass, and the color material concentration in the ink is high in the ink set. An ink jet recording method characterized in that the printing order is earlier. 3. The ink jet recording method according to claim 2, wherein the head used for printing is a line head. 4. The ink jet recording method according to claim 3, wherein the line head has a resolution of 360 dpi or more and a drive frequency of 7 kHz or more.