JP2007197635A - Ink set for inkjet and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set for inkjet and an inkjet recording method, wherein the curling and penetration in an ordinal recording paper are prevented, and even when a printing concentration is high, the amount of penetration is small. <P>SOLUTION: The ink set for two or more color inkjet comprises at least a coloring agent, an organic solvent and water, wherein a water content in each ink is 10-50 mass% to the total ink mass, at least one organic solvent is a water soluble organic solvent having an SP value of 16.5-24.6, a content of the organic solvent is 30 mass% or more to the total ink mass, an ink transfer amount is 15 ml/m<SP>2</SP>or more after 0.05 seconds contact time by a Bristow method, and the ink transfer amount is smaller as a printing order is earlier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  In recent years, the inkjet recording method can be easily and inexpensively produced images, and thus has been applied to various printing fields such as photographs, various printing, marking, special printing such as color filters, and the like. 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 special paper, there is a problem that a recording medium that can be used is limited and the cost of the recording medium 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 of the home or office. The printer also scans by moving the conventional inkjet head in the direction crossing 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 crossing 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 (the phenomenon that the printed ink passes through the recording medium and the image appears on the back), Various studies have been made 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, a so-called water-based ink in which water, which is generally used as an ink-jet ink, is a main component of a solvent, tends to curl on plain paper. This seems to occur because the hydrogen bond of cellulose on paper shifts from the original position after swelling, and various improvements have been studied, but it is still insufficient (see, for example, Patent Document 1).

  On the other hand, non-aqueous inks have a feature that they have little influence on hydrogen bonding of cellulose and are difficult to curl, and line printers using non-aqueous inks are also commercially available. (For example, refer to Patent Document 2).

  The present inventor has found an ink that can simultaneously prevent two problems that are in a trade-off relationship between curling and strike-through (see Patent Documents 3 to 6).

However, because the line printer has a higher processing speed than the serial printer, the overlap of the paper after printing becomes faster, so the ink penetration rate is increased to prevent the ink from overflowing on the paper surface to prevent the paper from being set over. Although it is necessary, simply taking a means for increasing the ink permeation speed is a problem because the ink permeates quickly into the interior, resulting in a low printing density and a large amount of show-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

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent curling and back-through in plain paper recording, and has a high printing density and low back-through, and an ink jet recording method. Is to provide.

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

1. An ink set for ink jet of two or more colors containing at least a coloring material, an organic solvent, and water, wherein the water content in each ink is 10% by mass or more and less than 50% by mass of the total ink mass In addition, at least one of the organic solvents is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and containing the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 The amount of ink is 30% by mass or more and 90% by mass or less of the total ink mass, the ink transfer amount after a contact time of 0.05 seconds by the Bristow method is 15 ml / m ² or more and 40 ml / m ² or less, and the ink transfer amount is An ink set for ink jet, characterized in that the earlier the printing order, the fewer the ink.

2. An ink jet recording method for printing using at least two colors of ink containing a coloring material, an organic solvent, and water, wherein the water content in each ink is 10% by mass or more and 50% by mass of the total ink mass And at least one of the organic solvents is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 The solvent content is 30% by mass or more and 90% by mass or less of the total ink mass, and the ink transfer amount after a contact time of 0.05 seconds by the Bristow method is 15 ml / m ² or more and 40 ml / m ² or less. An ink jet recording method characterized in that an ink having a smaller ink transfer amount is earlier in a printing order among inks.

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

  4). 3. The inkjet recording method according to 2, 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 provide an ink-jet ink set and an ink-jet recording method which prevent curling and show-through in plain paper recording and have a high printing density and little show-through.

  Hereinafter, although the best mode for carrying out the present invention will be described, the present invention is not limited to these.

The inventor of the present invention is an ink jet ink set of two or more inks containing at least a coloring material, an organic solvent, and water, wherein the water content in each ink is 10% by mass or more of the total ink mass, 50 Less than mass%, and at least one of the organic solvents 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 and less than 24.6. The content of the volatile organic solvent is 30% by mass or more and 90% by mass or less of the total ink mass, and the ink transfer amount after a contact time of 0.05 seconds by the Bristow method is 15 ml / m ² or more and 40 ml / m ² or less. By using a line printer with a head spacing of 2 cm, for example, an ink with a smaller ink transfer amount in the ink set, for example, using a line printer with a head spacing of 2 cm, the printing speed is about 100 ppm. It has been found that there is no set-off, the image density is high, and the show-through and curl can be reduced.

The inventor has found that the printing time interval between the inks is approximately 0.05 seconds under the above-described conditions, and if the ink is absorbed in an amount of 15 ml / m ² or more during that time, the settling does not occur. However, this alone has been a problem because the penetration of the ink into the inside is fast as described above, and the print density is low and the showthrough is increased. As a result of intensive studies, it has been found that in the line printer, the printing density, back-through, and back-off are greatly influenced by the permeation speed of each ink and the printing order. Further, it was found that by lowering the permeation speed of the ink in the earlier printing order, there is no settling and the printing density can be increased and the settling can be lowered.

The reason is as follows. The pigment in the ink tends to stay on the surface when the ink penetration rate is low, and easily penetrates into the interior when the ink penetration rate is high. If the ink permeation speed is low, there is a risk of ink overflow, but if the ink transfer amount after 0.05 seconds of contact time by the Bristow method is suppressed to 15 ml / m ² or more, there is no concern of ink overflow. Also, the lower the permeation speed, the lower the permeation speed of the ink in the earlier printing order, and the lowering of the set-off can be achieved because the pigment aggregates on the paper surface when the ink with the lower permeation speed is printed first. It is thought that this is because many of the pigments of the ink printed next tend to have affinity with the already agglomerated pigments, and also easily adhere to the paper surface.

  The ink transfer amount can be adjusted by adjusting the amount of the surfactant in the ink and the type and amount of the water-soluble organic solvent. For example, it can be adjusted by changing the addition amount of a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6.

  The Bristow method is a measurement method shown in “Japan TAPPI No. 51-87” (Paper and Pulp Technology Association, Paper Pulp Test Method No. 51-87, Bristow Method). In the present invention, Konica first class (manufactured by Konica Minolta Business Technologies, Inc.) was used as the plain paper used for the measurement. An automatic scanning liquid absorption meter KM500win (Kumaya Riki Kogyo Co., Ltd.) was used as a measuring device.

"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, it is excellent in emission stability and decap resistance, has good character quality of the formed image, good anti-through-through characteristics, and has good curl characteristics of the printed recording material. It becomes possible to do.

  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.

The solubility parameter (SP value) of the solvent referred to in the present invention is a value represented by the square root of the molecular aggregation energy, and is described in Polymer HandBook (Second Edition) Chapter IV Solubility Parameter Values. Unit is (MPa) ^1/2, it 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, 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. Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (SP value: 24.5)
Ethylene glycol monoethyl ether (SP value: 23.5)
Ethylene glycol monobutyl ether (SP value: 22.1)
Ethylene glycol monoisopropyl ether (SP value: 22.3)
Diethylene glycol monomethyl ether (SP value: 23.0)
Diethylene glycol monoethyl ether (SP value: 22.4)
Diethylene glycol monobutyl ether (SP value: 21.5)
Diethylene glycol diethyl ether (SP value: 16.8)
Triethylene glycol monomethyl ether (SP value: 22.1)
Triethylene glycol monoethyl ether (SP value: 21.7)
Triethylene glycol monobutyl ether (SP value: 21.1)
Propylene glycol monomethyl ether (SP value: 23.0)
Propylene glycol monophenyl ether (SP value: 24.2)
Dipropylene glycol monomethyl ether (SP value: 21.3)
Tripropylene glycol monomethyl ether (SP value: 20.4)
1,3-dimethyl-2-imidazolidinone (SP value: 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, etc. are 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.

<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. Multivalent metal ions are contained in sulfates, chlorides, nitrates, acetates, organic ammonium salts, EDTA 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.

<Ink transfer amount after 0.05 seconds contact time by Bristow method>
The amount of ink transferred after a contact time of 0.05 seconds by the Bristow method depends on physical properties such as the surface tension / viscosity of the ink and the contact angle between the ink and the paper capillary. These physical property values are affected by the type and amount of the material in the ink, such as the type and composition of the ink solvent, the type of dispersant, the type of surfactant, and the concentration. The type and amount of the material in the ink are also related to the dispersion stability and emission stability of the pigment in the ink.

Therefore, in the present invention, the ink transfer amount after a contact time of 0.05 seconds by the Bristow method is required to be 15 ml / m ² or more in order to prevent color bleeding in the line printer. In this case, priority is given to ensuring dispersion stability and emission stability, and the order of printing is determined by the amount of ink transfer determined as a result. The ink transfer amount can be adjusted by changing the type and amount of the material in the ink within a range that does not affect the dispersion stability and the emission stability.

  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.

Example 1
<Preparation of ink>
(Preparation of pigment dispersion)
(Preparation of yellow pigment dispersion)
The following additives were mixed, put together with 200 g of zirconia beads having a diameter of 0.5 mm into a polypropylene plastic bottle, sealed, and dispersed for 5 hours using a paint shaker. A magenta pigment having a yellow pigment content of 15%. A dispersion was prepared.

C. I. Pigment Yellow 120 15 parts Dispersyk190 (Byk-Chemie)
(40% solid content aqueous solution) 15 parts Tripropylene glycol monomethyl ether 55 parts Water 15 parts (Preparation of magenta pigment dispersion, cyan pigment dispersion, and black pigment dispersion)
In the preparation of the yellow pigment dispersion, C.I. I. In place of Pigment Yellow 120, C.I. I. Pigment red 122 (magenta pigment dispersion), C.I. I. Pigment blue 15: 3 (cyan pigment dispersion), C.I. I. 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-1 to a-7]
Tripropylene glycol monomethyl ether and water were added to the yellow pigment dispersion prepared above so that the pigment concentration in the ink was 4% and tripropylene glycol monomethyl ether / water = 7/3, and the mixture was sufficiently stirred. Next, this mixed solution was filtered with a # 3500 mesh metal filter, deaerated with a hollow fiber membrane, and ink was prepared. The ink transfer amount after a contact time of 0.05 seconds by the Bristow method was 18 ml / m ² .

  Tripropylene glycol monomethyl ether added to each color pigment dispersion using the fact that increasing the tripropylene glycol monomethyl ether in the ratio of tripropylene glycol monomethyl ether increases the ink transfer amount, and increasing the water ratio decreases the ink transfer amount. The amount of ether and water was changed so that the water content was 10% by mass or more and less than 50% by mass of the total ink mass, and the content of tripropylene glycol monomethyl ether was 30% by mass or more of the ink mass. By changing the ratio of propylene glycol monomethyl ether / water, Y (yellow), M (magenta), C (cyan), and K (black) inks having different ink transfer amounts were produced.

[Preparation of ink set b]
As a solvent for each color pigment dispersion of ink set a-1, it was dispersed using 70 parts of tripropylene glycol monomethyl ether without using water, and only tripropylene glycol monomethyl ether was added so that the pigment concentration was 4%. In the same manner as in ink set a-1, Y (yellow), M (magenta), C (cyan), and K (black) inks were produced.

[Preparation of ink set c]
Y (yellow), M (magenta), C (cyan) in the same manner as ink set a-1, except that a solvent was added to the pigment dispersion so that tripropylene glycol monomethyl ether / water in the ink was 2/8. ), K (black) ink.

[Preparation of ink set d]
Y (yellow), M (magenta), C (cyan), and ink set a-1 except that the tripropylene glycol monomethyl ether in the pigment dispersion and the ink was changed to diethylene glycol (SP value 30.6). A K (black) ink was prepared.

<< Preparation of image recording sample >>
The number of nozzles per head is 512, the resolution is 360 dpi (dpi represents the number of dots per 2.54 cm), the amount of droplets is 14 pl, and the drive frequency so that the nozzles are arranged at right angles on the belt conveyor in the direction of travel. Four 12.8 kHz piezo-type heads (Konica Minolta IJ) are arranged so that the distance between the nozzles of adjacent heads is 20 mm, and Konica First Class (Konica Minolta Business Technologies, Inc., plain paper) is used. The ink was placed on a belt conveyor and conveyed at a speed of 350 mm / sec, and four colors of ink were printed in the order shown in Table 1 using four heads.

[Evaluation of printing density]
Using ink set a-1, the four colors Y, M, C, and K were combined to produce gray. Subsequently, with respect to the gray produced with the ink set a-1, the ink sets a-2 to a-7 are used to adjust the emission amounts of the Y, M, C, and K inks so that the color and density are equal. I made it. At this time, Table 1 shows inks in which the emission amount is added to the emission amounts of the Y, M, C, and K inks using the ink set a-1. The addition of the emission amount indicates that the pigment in the ink has penetrated into the inside as compared with the ink set a-1.

[Evaluation of setback]
Is there any transfer of ink from the solid print part on the back side of the white background of the overlapped sample for the printed sample that is printed 200 sheets of the above solid print image continuously and overlaid on the discharge tray? It was judged by visual observation.

A: No transfer of ink to the other back of the sample was observed. B: Slight ink transfer was observed. C: Weak ink transfer was observed. D: Strong ink transfer was observed. Evaluation of〕
The back side of the solid-printed sample of each color on the plain paper (Konica first class) was visually observed, and the through-through resistance was evaluated according to the following criteria.

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 is a quality that is anxious when printing on the back side D: Ink bleed or back-through is significantly recognized on the back side, and is an unacceptable quality for back side printing [Evaluation of curling resistance]
About the curl when each color was printed on the above-mentioned plain paper (Konica first class) for each color, 10cm x 10cm area, and the sample was left in the environment for one day to measure the curl. The evaluation was performed 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 Table 1 shows the above results for the quality that is a problem in practical use.

From Table 1, it can be seen that printing density, set-off, show-through resistance, and curl resistance are good by printing in ascending order of ink transfer amount as in the present invention. On the other hand, when printing is performed in the order of the higher ink transfer amount, the ink printed earlier tends to enter the inside, so that the through-through resistance is deteriorated and the print density is lowered unless the print amount is increased. However, it can be seen that when the ink transfer amount is less than 15 ml / m ² , the penetration of the ink into the paper is too slow, so that the back-off to another paper is likely to occur.

<< Evaluation of Ink Set a-1, Ink Set b, Ink Set c, Ink Set d >>
For each of ink set a-1, ink set b, ink set c, and ink set d,
<< Preparation of image recording sample >>
The number of nozzles per head is 512, the resolution is 360 dpi (dpi represents the number of dots per 2.54 cm), the amount of droplets is 14 pl, and the drive frequency so that the nozzles are arranged at right angles on the belt conveyor in the direction of travel. Four 12.8 kHz piezo-type heads (Konica Minolta IJ) are arranged so that the distance between the nozzles of adjacent heads is 20 mm, and Konica First Class (Konica Minolta Business Technologies, Inc., plain paper) is used. The ink was placed on a belt conveyor and conveyed at a speed of 350 mm / sec, and four colors of ink were printed as shown in Table 2 by four heads.

[Evaluation of through-hole resistance]
The back side of the solid-printed sample of each color on the plain paper (Konica first class) was visually observed, and the through-through resistance was evaluated according to the following criteria.

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 is a quality that is anxious when printing on the back side D: Ink bleed or back-through is significantly recognized on the back side, and is an unacceptable quality for back side printing [Evaluation of curling resistance]
About the curl when each color was printed on the above-mentioned plain paper (Konica first class) for each color, 10cm x 10cm area, and the sample was left in the environment for one day to measure the curl. The evaluation was performed 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 However, it is a quality that is a problem in practice. [Evaluation of suitability for intermittent emission]
Intermittent operation of continuous discharge for 10 seconds → pause for a fixed time → continuous discharge was performed. At this time, since whether or not the discharge direction is disturbed at the beginning after the discharge pause is determined by the length of the pause time, the stability of intermittent discharge is measured by changing the length of the discharge pause time stepwise. The evaluation was based on the following criteria. The evaluation was performed at an environmental temperature of 23 ° C. and a humidity of 55% RH.

A: Stable discharge even after 31 to 45 seconds B: Stable discharge even after 21 to 30 seconds C: Stable discharge even after 11 to 20 seconds D: Stable discharge for 10 seconds or less The above results are shown in Table 2.

  From Table 2, when the amount of water-soluble organic solvent is large and the amount of water is low beyond the range of the present invention as in ink set b, the penetration resistance deteriorates. Conversely, when the ink set c exceeds the range of the present invention and has a large amount of water and a small amount of water-soluble organic solvent, curling resistance and suitability for intermittent emission deteriorate. It can also be seen that when the SP value of the water-soluble organic solvent is high beyond the range of the present invention, the curl resistance and suitability for intermittent emission deteriorate.

Claims (4)

An ink set for ink jet of two or more colors containing at least a coloring material, an organic solvent, and water, wherein the water content in each ink is 10% by mass or more and less than 50% by mass of the total ink mass In addition, at least one of the organic solvents is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and containing the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 The amount of ink is 30% by mass or more and 90% by mass or less of the total ink mass, the ink transfer amount after a contact time of 0.05 seconds by the Bristow method is 15 ml / m ² or more and 40 ml / m ² or less, and the ink transfer amount is An ink set for ink jet, characterized in that the earlier the printing order, the fewer the ink. An ink jet recording method for printing using at least two colors of ink containing a coloring material, an organic solvent, and water, wherein the water content in each ink is 10% by mass or more and 50% by mass of the total ink mass And at least one of the organic solvents is a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, and the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 The solvent content is 30% by mass or more and 90% by mass or less of the total ink mass, and the ink transfer amount after a contact time of 0.05 seconds by the Bristow method is 15 ml / m ² or more and 40 ml / m ² or less. An ink jet recording method characterized in that an ink having a smaller ink transfer amount is earlier in a printing order among inks. The inkjet recording method according to claim 2, wherein the head used for printing is a line head. 3. The ink jet recording method according to claim 2, wherein the line head has a resolution of 360 dpi or more and a driving frequency of 7 kHz or more.