JP2005220298A - Inkjet ink and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inkjet ink which has good letter reproducibility on a plain paper, is suppressed in strike-through in a recording medium and curl after recording, exhibits rapid penetration and drying on the plain paper and is excellent in high-speed printing characteristics, and an inkjet recording method using the inkjet ink. <P>SOLUTION: The inkjet ink comprises a colorant and a solvent, where the solvent contained in the inkjet ink gives a ΣS, defined by equations (1) and (2) below, of at least 6 and less than 35, and contains water in an amount of at least 10 mass% and less than 45 mass%: equation (1) S=H/M×1,000 (wherein H is the total number of hydroxyl groups and amino groups per molecule and M is the molecular weight); and equation (2) ΣS=S<SB>1</SB>×C<SB>1</SB>+...+S<SB>n</SB>×C<SB>n</SB>(wherein S<SB>1</SB>is S of solvent 1; C<SB>1</SB>is the mass fraction of the solvent 1 in the ink; S<SB>n</SB>is S of the solvent n; and C<SB>n</SB>is the mass fraction of the solvent n in the ink). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink-jet ink which is difficult to cause character reproducibility, back-through, curl, and the like on plain paper, and has excellent penetration and drying on paper and high-speed printability, and an ink-jet recording method using the ink-jet ink About.

  In recent years, the ink jet recording system 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, a recording device that emits and controls fine dots, ink that has improved color reproduction gamut, durability, and emission suitability, and ink absorbability, coloring material color development, surface gloss, etc. have been dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper.

  However, in an inkjet system that requires special paper, there is a problem that the recording medium that can be used is limited, the cost of the recording medium is increased, and the like.

  On the other hand, in the office, there is an increasing need for a system capable of performing full color printing at high speed without being restricted by a recording medium (for example, plain paper, coated paper, art paper, plain paper double-sided printing, etc.).

  Various studies have also been made on the composition of the ink-jet ink from the viewpoints of printing at high speed, good character reproducibility on plain paper and less curling, fast penetration into paper and quick drying.

  Solvent-based inks that can perform printing at high speed are also being studied. That is, by using an oil-based ink (solvent ink jet ink) that contains a volatile solvent and has improved drying properties, even when printing on plain paper, the penetration into the recording medium is fast and the drying time is short. High-speed printing is possible without curling or the like. However, solvent-based inks have strong penetrability into plain paper media, so that the character reproducibility is poor, and the so-called back-through defect is a phenomenon in which ink is discharged from the back of the recording medium and seen from the back. .

  On the other hand, when water-based ink with a high water content is used, the character reproducibility is good on plain paper, and the above-described back-through is also good, but the drying time with water in the ink is long. In addition, it is unsuitable for high-speed printing, and water-based inks have a drawback that the recording medium tends to curl.

  In order to solve the above problems, an ink jet recording method using an ink having improved penetrability by specifying a wetting time and an absorption coefficient for a recording medium in the Bristow method has been disclosed (for example, see Patent Document 1). However, in this method, since the colorant in the ink also penetrates into the plain paper at the same time, the image density is lowered and the ink shows through, which is not suitable for double-sided printing. Have

  Further, an inkjet ink containing a specific amide compound, pyridine derivative, imidazoline compound or urea compound as an anti-curl agent is disclosed (for example, see Patent Document 2). However, this method has a problem that clogging is likely to occur in the nozzle portion of the recording head as the ink liquid is dried.

  As a method for improving the curl, an ink jet recording method has been proposed in which a solution containing water is applied to the back side of the image printing surface to optimize the curl balance (see, for example, Patent Document 3). However, this method has the disadvantages that it does not have double-sided recording suitability, and the strength of plain paper decreases with the increase in the amount of ink and curl balance liquid attached to plain paper, and jamming or the like tends to occur during transportation. there were.

As described above, in plain paper recording, there is a trade-off between show-through and curl, and until now no ink has sufficiently satisfied these characteristics.
JP 10-316915 A JP 9-176538 A JP-A-10-272828

  Therefore, the present invention has good character reproducibility on plain paper, suppresses back-through of the recording medium, and also suppresses curling after recording, so that permeation and drying on plain paper is fast, and high-speed printing characteristics are achieved. An object is to obtain an excellent ink jet ink and an ink jet recording method using the ink jet ink.

  The above object of the present invention is achieved by the following means.

(Claim 1)
In an inkjet ink containing a colorant and a solvent,
When ΣS defined by the following formulas (1) and (2) was determined for the solvent contained in the inkjet ink, the value was 6 or more and less than 35, and the solvent contained 10% by mass or more of water, An ink-jet ink containing less than 45% by mass.

Formula (1) S = H / M × 1000
H: Total number of hydroxyl groups and amino groups per solvent molecule
M: Molecular weight of solvent Formula (2) ΣS = S ₁ × C ₁ + S ₂ × C ₂ + S ₃ × C ₃ ... + S _n × C _n
S ₁ : S of solvent 1, C ₁ : mass fraction in ink of solvent 1
S _n : S of solvent n, C _n : Mass fraction in ink of solvent n (Claim 2)
2. The inkjet ink according to claim 1, wherein a value of ΣS defined by the formula (2) is 6 or more and less than 25. 3.

(Claim 3)
The inkjet ink according to claim 1, wherein the inkjet ink contains a surfactant and the content of the surfactant is less than 1% by mass.

(Claim 4)
The inkjet ink according to claim 3, wherein the content of the surfactant is less than 0.1% by mass.

(Claim 5)
The sum of the content of the solvent whose value of S defined by said Formula (1) is 25 or more and less than 55 is less than 10 mass%, It is any one of Claims 1-4 characterized by the above-mentioned. Inkjet ink.

(Claim 6)
6. The inkjet ink according to claim 5, wherein the total content of solvents having a value of S defined by the formula (1) of 25 or more and less than 55 is less than 5% by mass.

(Claim 7)
The inkjet ink according to any one of claims 1 to 6, wherein the surface tension is 25 mN / m or more and 35 mN / m or less.

(Claim 8)
The inkjet ink according to any one of claims 1 to 7, further comprising a pigment as a colorant.

(Claim 9)
An inkjet recording method, comprising: discharging the inkjet ink according to any one of claims 1 to 8 by an inkjet head and printing on plain paper.

(Claim 10)
An ink jet recording method comprising: discharging the ink jet ink according to any one of claims 1 to 8 by an ink jet head, and printing at a recording speed of 5 m / min or more in the sub-scanning direction.

(Claim 11)
An ink jet recording method comprising: discharging the ink jet ink according to any one of claims 1 to 8 by an ink jet head, and printing on both surfaces of a recording medium.

  According to the present invention, it is possible to obtain an inkjet ink capable of performing high-speed printing on plain paper, having less curl and set-off, and obtaining excellent print quality, and an inkjet recording method using the inkjet ink.

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

  As mentioned above, in plain paper recording, there is a trade-off between show-through and curl, and water-based inks with high water content have good character reproducibility and suppression of show-through, but have the disadvantage that curl is likely to occur. is there. On the other hand, in oil-based inks that do not contain water, curling is unlikely to occur, but character reproducibility is poor and ink back-through is likely to occur.

  The present inventors have made the trade-off by controlling the water content of the solvent contained in the ink-jet ink and selecting the characteristics of each solvent used in the ink using parameters related to the structure of each solvent. Thus, an ink-jet ink capable of obtaining good printing characteristics even when used on plain paper capable of eliminating the above relationship could be obtained. That is, in the ink-jet ink containing a colorant and a solvent, the ink solvent contains 10% by mass or more and less than 45% by mass of water, and the solvent contained in the ink-jet ink contains the following formulas (1) and (2). When the ΣS defined by the above is obtained, when the value is 6 or more and less than 35, more preferably 6 or more and less than 25, the ink-jet ink exhibits good character reproducibility, and show-through is prevented, And we found that curling can be suppressed on plain paper.

  By setting the water content in the ink to 10% by mass or more, good character reproducibility is exhibited and back-through is prevented, and the water content is less than 45% by mass, and the following formula (1), Curling can be prevented by setting the parameter ΣS of the solvent defined by (2) to 6 or more and less than 35, more preferably 6 or more and less than 25.

Formula (1) S = H / M × 1000
Here, H: total number of hydroxyl groups and amino groups per molecule of solvent M: molecular weight of solvent.

Equation (2) ΣS = S ₁ × C ₁ + S ₂ × C ₂ +... + S _n × C _n
Here, S ₁ : S of solvent 1, C ₁ : Mass fraction of ink in solvent 1 S ₂ : S of solvent 2, C ₂ : Mass fraction of solvent 2 in ink _Sn : Solvent n S, C _n : The mass fraction of the solvent n in the ink.

(About S value)
The S value will be specifically described.

As defined above, the S value is a hydroxyl group (—OH) and an amino group (—NH—, —NH ₂ , —N ⁺ H ₃ (ammonio group)), and the number is counted as one. To do.

For example, ethylene glycol is
HO—CH ₂ CH ₂ —OH, ₂ hydroxyl groups (—OH), 0 amino groups, etc., molecular weight 62.1, S value is
2 ÷ 62.1 × 1000 = 32.2
Triethanolamine is
N (CH ₂ CH ₂ OH) ₃ , ₃ hydroxyl groups (—OH), no amino groups, etc., molecular weight 149, S value is
3 ÷ 149 × 1000 = 20.1
2-pyrrolidone is
(—C (═O) —NH—CH ₂ CH ₂ CH ₂ —), one amino group (—NH—), a molecular weight of 85.1, and the S value is
1 ÷ 85.1 × 1000 = 11.7
Water
H—O—H 1, one hydroxyl group (—OH) (defined as), a molecular weight of 18, and the S value is
1 ÷ 18 × 1000 = 55.6
As described above, the S value of the organic solvent or water can be calculated as described above.

  In the present invention, the S value of each solvent used in the ink thus calculated is obtained, and based on this, the solvent and the solvent ratio are set so that the ΣS of the solvent in the ink falls within a predetermined range as described above. By selecting and controlling the water content within a certain range, the inkjet ink of the present invention can be obtained. Preferably, in addition to these, a more preferable effect can be obtained by keeping the amount of the active agent or the solvent having a large S value below a certain level.

  In the ink-jet ink of the present invention (hereinafter also simply referred to as ink), the content of the surfactant in the ink is also related to the above-described back-through and curl, and preferably the content of the surfactant is 1 It is less than mass%, more preferably less than 0.1 mass%.

  Further, the content of the solvent in which the S value in the above-described formula (1) is 25 or more and less than 55 is also correlated with the curl, and the total content in the ink is less than 10% by mass, preferably less than 5% by mass. Preferably there is. When the total content of these activators and solvents is high, curling is likely to occur, and surfactants and solvents with the S value of 25 or more and less than 55 tend to interact with cellulose, which is paper fibers, through hydrogen bonding. It is estimated that this will cause curling.

  In addition, the ink of the present invention is one of the features that both the permeability and the drying property are excellent. In recent years, so-called line heads having the same width as the recording medium have been developed, and printing can be performed at a higher speed than conventional shuttle type heads. In such a recording apparatus, it is easy to cause a problem that the previous printed portion is transferred to the back side when the discharged printed materials are stacked, and the ink is required to have quick permeability and quick drying. The ink of the present invention has good penetrability, quick drying, a short time for ink to remain on the surface of the recording medium, and exhibits particularly high suitability in a printing method having a high recording speed as described above. That is, it is suitable for printing at a recording speed of 5 m / min or more with respect to the sub-scanning direction (paper feeding direction).

  The ink of the present invention is also effective when printing on both sides of a recording medium. In double-sided printing, after recording on one side, the recording medium is often turned over and transported with the printing surface facing down. However, the ink of the present invention has the above-mentioned characteristics. There is no contamination with ink.

  In the ink of the present invention, if the amount of water is less than the specified amount, there will be a lot of showthrough and bleeding of characters, and if it is more than the specified amount, curling tends to occur. Regarding ΣS, if this is small, the system becomes hydrophobic, water cannot be sufficiently dissolved and ink cannot be produced, and if it is too large, curling tends to occur.

  Usually, the surface tension of the ink-jet ink is in the range of 37 mN / m to 55 mN / m. However, in the present invention, the surface tension is particularly preferably in the range of 25 to 35 mN / m. The ink has better drying properties. This makes the ink suitable for high-speed printing with the necessary penetrability and dryness when printing on plain paper using a head capable of high-speed printing, such as the above-mentioned line head, and at the same time without any set-off or back-through. It becomes. The surface tension is measured by a Wilhelmy surface tension meter in an environment with a relative humidity of 55% and 23 ° C.

  The ink-jet ink of the present invention comprises a colorant in the above-mentioned solvent, and further contains additives as described later, and the hue of the colorant used in the present invention is yellow, magenta, cyan Black, blue, green, and red are preferably used, and yellow, magenta, cyan, and black colorants are particularly preferable.

  In the present invention, a dye ink in which the colorant is a water-soluble dye, or a pigment ink that is a pigment in which the colorant is insoluble in a solvent constituting the inkjet ink and forms a fine dispersion, or a colorant is used. Even in the case of a dispersion ink comprising a dispersion of a colored polymer, basically, as described above, paying attention to the solvent system, the above formulas (1) and (2), the water content, etc. Therefore, the colorant is not limited to any kind and can be applied to various ink-jet inks.

  Examples of water-soluble dyes 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 specific compounds thereof. Examples thereof include the dyes exemplified in JP-A No. 2002-264490.

  In addition, oil-soluble dyes that form colored fine particles together with the polymers and the like and become colorants are usually soluble in organic solvents having no water-soluble groups such as carboxylic acid and sulfonic acid, and are insoluble in water, such as disperse dyes. Etc. are selected. Moreover, the dye which shows oil solubility by salt-forming a water-soluble dye with a long-chain base is also contained. For example, acid dyes, direct dyes, and salt-forming dyes of reactive dyes and long chain amines are known.

  However, in the present invention, it is preferable to use a pigment as the colorant, and the pigment that does not have solubility in the solvent system is used for hydrogen bonding to the plain paper (cellulose) of the solvent system. Affinity is preferable because it hardly changes depending on the colorant and is easy to control.

  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 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, 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. Pigment Orange 43;
C. I. Vat Violet 3;
C. I. Pigment Violet 19, 23, 37;
C. I. Pigment Green 36, 7;
C. 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 can be mentioned. The pigment used in the present invention is preferably used after being dispersed by a dispersing machine together with a dispersant and other necessary additives according to various desired purposes. As the disperser, conventionally known ball mills, sand mills, attritors, roll mills, agitators, Henschel mixers, colloid mills, ultrasonic homogenizers, pearl mills, wet jet mills, paint shakers and the like can be used.

  In the present invention, a polymer dispersant can be used in the dispersion of the pigment. Examples of the polymer dispersant used in the present invention include acrylic ester copolymers, styrene / acrylic ester copolymers, butyral resins obtained by acetalizing partially saponified polyvinyl alcohol, resins such as vinyl acetate copolymers, etc. An alkylene glycol resin such as polyethylene glycol, a rosin resin, a salt of a high molecular weight polycarboxylic acid, a salt of a long-chain polyaminoamide and a polar acid ester, a high molecular weight unsaturated acid ester, a polymer copolymer, a modified polyurethane, Modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonyl phenyl ether, stearylamine acetate, pigment Invitation Body or the like can also be mentioned. In particular, acrylic acid ester copolymers, styrene / acrylic acid ester copolymers, butyral resins, and polyvinyl alcohol triethylene glycol are preferable.

  Examples of these include ESREC BL-1, BM-1, etc. (butyral resin; manufactured by Sekisui Chemical Co., Ltd.), polyethylene glycol PEG6000S (Sanyo Chemical Co., Ltd.), and acrylic resin Collacral P (manufactured by BASF). Examples include rosin resins; lime resin (Arakawa Chemical Industries), sodium polyacrylate Acrysol GS (Rohm & Haas), polyvinyl alcohol, and the like.

Specific examples other than the above include the following.
BYK Chemie's “Anti-Terra-U (polyaminoamide phosphate)”, “Anti-Terra-203 / 204 (high molecular weight polycarboxylate)”, “Disperbyk-101 (polyaminoamide phosphate and acid ester),” 107 (hydroxyl group-containing carboxylic acid ester), 110 (copolymer containing an acid group), 130 (polyamide), 161, 162, 163, 164, 165, 166, 170 (polymer copolymer) ”,“ 400 ” , “Bykumen” (high molecular weight unsaturated acid ester), “BYK-P104, P105 (high molecular weight unsaturated acid polycarboxylic acid)”, “P104S, 240S (high molecular weight unsaturated acid polycarboxylic acid and silicon-based)”, “Lactimon (long chain amine and unsaturated acid polycarboxylic acid and silicon)”.

  Also, “Efka CHEMICALS” “Efka 44, 46, 47, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766”, “Efka Polymer 100 (modified polyacrylate), 150 (aliphatic) System modified polymer), 400, 401, 402, 403, 450, 451, 452, 453 (modified polyacrylate), 745 (copper phthalocyanine system) "," Kyoeisha Chemical Co., Ltd. "" Floren TG-710 (urethane oligomer) "," “Flonon SH-290, SP-1000”, “Polyflow No. 50E, No. 300 (acrylic copolymer)”, “Disparon KS-860, 873SN, 874 (polymer dispersing agent), # 2150, manufactured by Enomoto Kasei Co., Ltd. (Aliphatic polyvalent carboxylic acid), # 7004 (polyether ester type) ” It is done.

  Furthermore, “Demol RN, N (Naphthalenesulfonic acid formalin condensate sodium salt), MS, C, SN-B (aromatic sulfonic acid formalin condensate sodium salt), EP”, “Homogenol L-18 (Polyethylene)” manufactured by Kao Corporation Carboxylic acid type polymer) "," Emulgen 920, 930, 931, 935, 950, 985 (polyoxyethylene nonyl phenyl ether) "," Acetamine 24 (coconut amine acetate), 86 (stearyl amine acetate) ", General Corporation "Solspers 5000 (phthalocyanine ammonium salt type), 13240, 13940 (polyesteramine type), 17000 (fatty acid amine type), 24000, 32000", Nikko Chemical's "Nikkor T106 (polyoxyethylene sorbitan monooleate), MY" -IEX (polyoxyethylene monostearate), Hexagline 4-0 (hexaglyceryl ruthenate Huwei rate) ", and the like.

  As the polymer dispersant, it is preferable from the viewpoint of dispersion stability to use a polymer having a molecular weight of 2,000 to 100,000, preferably 3,000 to 10,000. These resins are preferably used in an amount of about 0.1% by mass to 100% by mass, preferably 1% by mass to 60% by mass with respect to the pigment. Increasing the viscosity will increase the viscosity of the ink. In addition, the measurement of the molecular weight in this invention is the number average molecular weight calculated | required in polystyrene conversion by the universal calibration method using high temperature GPC (gel permeation chromatography) and molecular weight.

  The average particle size of the pigment dispersion used in the ink of the present invention is preferably 10 nm to 200 nm, more preferably 10 nm to 100 nm, and still more preferably 10 nm to 50 nm. If the average particle size of the pigment dispersion exceeds 100 nm, the dispersion becomes unstable. In addition, even when the average particle size of the pigment dispersion is less than 10 nm, 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 device using a light scattering method, an electrophoresis method, a laser Doppler method or the like. It is also possible to obtain a particle image with a transmission electron microscope on at least 100 particles and perform statistical processing on the image using image analysis software such as Image-Pro (manufactured by Media Cybernetics). Is possible.

  In the inkjet ink of the present invention, a surfactant can also be used as an additive during dispersion. As the surfactant used in the present invention, any of cationic, anionic, amphoteric and nonionic can be used. The addition amount of the surfactant is adjusted so that the surface tension is 25 mN / m to 55 mN / m, more preferably 25 to 35 mN / m in the ink of the present invention as described above. preferable.

  Examples of the cationic surfactant include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, imidazolinium salts, and the like.

  Examples of the anionic surfactant include fatty acid soap, N-acyl-N-methylglycine salt, N-acyl-N-methyl-β-alanine salt, N-acyl glutamate, acylated peptide, alkyl sulfonate, Alkylbenzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfoacetate, α-olefin sulfonate, N-acylmethyl taurine, sulfated oil, higher alcohol sulfate, secondary higher alcohol Sulfate ester, alkyl ether sulfate, secondary higher alcohol ethoxy sulfate, polyoxyethylene alkyl phenyl ether sulfate, monoglyculate, fatty acid alkylolamide sulfate, alkyl ether phosphate ester, alkyl phosphate ester Examples include tellurium salts.

  Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate, imidazolinium betaine and the like.

  Nonionic activators include polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester, Oxyethylene 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, polyoxyethylene Fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide, acetyl Glycol, acetylene alcohol, and the like.

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

  The ink of the present invention uses water or a water-soluble organic solvent as a main liquid medium component as a solvent as described above. That is, when the ink solvent contains 10% by mass or more and less than 45% by mass of water, and ΣS defined by the above formulas (1) and (2) is obtained for the solvent contained in the inkjet ink, When the value is 6 or more and less than 35, that is, calculate ΣS from the S value of the solvent used and the mass fraction C in the ink, and use the solvent so that these values are in the above range. Thus, the effect of the present invention can be obtained.

  The organic solvent used as the ink solvent is selected from the following water-soluble organic solvents. Alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols (eg, ethylene glycol, diethylene glycol, Triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether , Ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol mono Ethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol dimethyl ether, etc.), amines (eg, ethanolamine, diethanolamine, triethanolamine, -Methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (for example, formamide , N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocyclic rings (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2-oxazolidone, 1,3 -Dimethyl-2-imidazolidinone etc.), sulfoxides (eg dimethyl sulfoxide etc.), sulfones (eg sulfolane etc.), sulfonates (eg sodium 1-butanesulfonate) Salt), urea, acetonitrile, acetone and the like. In the present invention, alkylene glycol monoethers or alkanediols are preferable, and alkylene glycol monoethers are more preferably ethylene. Glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, and alkanediols are 1,2-hexanediol or 1,2-pentanediol, particularly preferably , Triethylene glycol monobutyl ether, 1,2-hexanediol, and 1,2-pentanediol are preferable. In particular, those water-soluble organic solvents (when water is included as a solvent, water is also included) are contained in the ink so that the ΣS is 6 or more and less than 35.

  The total content of the water-soluble organic solvent in the ink differs depending on the S value of the solvent used, and cannot be specified unconditionally. Of the ink solvents composed of the water-soluble organic solvent and water, generally 40 to 95 masses. %, Particularly 60 to 90% by mass is preferred.

  In the ink-jet ink of the present invention, the total content of calcium ions, magnesium ions and iron ions, which are polyvalent metal ions of the ink, is preferably 10 ppm or less, more preferably 0.1 to 5 ppm, Most preferably, it is 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 ion according to the present invention is contained in sulfates, chlorides, nitrates, acetates, organic ammonium salts, EDTA salts and the like.

  In addition to the above description, the inkjet ink of the present invention is publicly known depending on the purpose of improving the emission stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Various additives, such as viscosity modifiers, specific resistance regulators, film forming agents, UV absorbers, antioxidants, anti-fading agents, anti-fouling agents, rust inhibitors, etc. can be appropriately selected and used, For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376. , Whitening agents described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771 and JP-A-4-219266. An agent etc. can be mentioned.

When forming an image by ejecting the ink-jet ink of the present invention, the ink-jet head used may be an on-demand system or a continuous system. In addition, 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) Type, bubble jet (R) type, etc.)
Any discharge method may be used.

  In the image forming method using the ink-jet ink of the present invention, for example, the ink jet ink is ejected as droplets from the ink-jet head based on the digital signal and attached to the ink receiver by using a printer or the like loaded with the ink-jet ink. An ink jet print in which an ink jet recording image is formed on the image recording medium is obtained.

  As the inkjet image recording medium, for example, any of plain paper, coated paper, cast coated paper, glossy paper, glossy film, and OHP film can be used. For example, a recording medium coated with a recording liquid receiving layer having a so-called void layer in which a porous layer is formed may be used, but plain paper typified by office paper such as copy paper is inexpensive. In addition, the recording medium used in the inkjet ink of the present invention is preferable because the ink characteristics can be sufficiently exhibited (printing quality is good, there is no show-through, and wrinkles and curls are small after printing).

  The plain paper is preferably 80 to 200 [mu] m uncoated paper belonging to a part of uncoated paper, special printing paper and information paper. Examples of the plain paper of the present invention include, for example, high-grade printing paper, intermediate-grade printing paper, lower-grade printing paper, thin-like printing paper, fine-coating printing paper, special printing paper such as fine-quality printing paper, foam paper, PPC paper, and other information paper Specifically, there are the following papers and various modified / processed papers using them, but the present invention is not particularly limited to these.

  High quality paper and colored high quality paper, recycled paper, copy paper / colored paper, OCR paper, carbonless paper / colored paper, synthetic paper such as YUPO 60, 80, 110 microns, YUPO COAT 70, 90 microns, etc. Coated paper 90kg, Foam mat paper 70, 90, 110kg, Foamed PET 38 microns, Mitsuori-kun (above, Kobayashi recording paper), OK fine paper, New OK fine paper, Sunflower, Phoenix, OK Royal White, Export fine paper ( NPP, NCP, NWP, Royal White) OK Book Paper, OK Cream Book Paper, Cream Premium Paper, OK Map Paper, OK Ishikari, Cucumber, OK Foam, OKH, NIP-N (above, Shin Oji Paper), Gold Wang, Toko, export quality paper, special demand quality paper, book paper, book paper L, light cream book paper, trilogy subject Paper, continuous slip paper, high quality NIP paper, silver ring, gold yang, gold yang (W), bridge, capital, silver ring book, harp, harp cream, SK color, securities paper, opera cream, opera, KYP medical record, silvia HN, Excellent Foam, NPI Foam DX (Nippon Paper), Pearl, Kinryo, Uscream fine paper, Special Book Paper, Super Book Paper, Book Paper, Diamond Foam, Inkjet Foam (Mitsubishi Paper), Carpet V, carpet SW, white elephant, luxury publication paper, cream carpet, cream white elephant, securities / voucher paper, book paper, map paper, copy paper, HNF (above, Hokuetsu), phone book cover, Book paper, cream shiorai, cream shiorai medium luff, cream shiorai large luff, DSK (above, Daishowa Paper), Sendai MP fine paper Jinjiang, Thunderbird fine, hanging paper, colored paper base, dictionary paper, cream book, white book, cream fine paper, map paper, continuous slip paper (above, Chuetsu Pulp), OP gold cherry (chuetsu), gold sand, reference book paper, Replacement certificate paper (white), form printing paper, KRF, white foam, color foam, (K) NIP, fine PPC, Kishu inkjet paper (made by Kishu Paper), Taiou, Bright Foam, Kant, Kant White, Dante, CM paper, Dante comic, Heine, paperback book paper, Heine S, New AD paper, Utrillo Excel, Excel Super A, Kant Excel, Excel Super B, Dante Excel, Heine Excel, Excel Super C, Excel Super D, AD Excel, Excel Super E, New Bright Foam, New Bright NI P (above Daio Paper), Sun Ring, Moon Ring, Unzen, Galaxy, Baiyun, Weiss, Moon Ring Ace, Baiyun Ace, Unzen Ace (above Nippon Paper Industries), Taiou, Bright Foam, Brightnip (above) Nagoya Pulp), Peony A, Gold Pigeon, Special Peony, White Peony A, White Peony C, Silver Pigeon, Super White Peony A, Light Cream White Peony, Special Medium Quality Paper, White Pigeon, Super Medium Quality Paper, Blue Pigeon, Red Pigeon, Gold Pigeon M Snow Vision, Snow Vision, Gold Pigeon Snow Vision, White Pigeon M, Super DX, Hamanasu O, Red Pigeon M, HK Super Printing Paper (above Honshu Paper), Stalinden (A / AW), Star Elm, Star Maple, Star Laurel, Star Poplar, MOP, Star Cherry I, Cherry I Super, Cherry II Super, Star Cherry III, Star Cherry IV, Cherry III Super, Cherry IV Sue Over (more than made Marusumiseishi), SHF (more than manufactured by Toyo pulp), TRP (all manufactured by Tokai pulp), Konica copy paper NR-A100 (manufactured by Konica Minolta Business Technologies, Inc.).

  Examples of the recording medium include high-quality paper and color high-quality paper, inkjet plain paper and special paper, recycled paper, and slip paper. Paper having a film thickness of 80 to 200 μm, which is widely used as ordinary plain paper, is particularly preferable for the purpose of the present invention.

  The ink-jet ink of the present invention can perform high-speed printing on plain paper as described above, has excellent penetrability and dryness, and unlike ordinary ink, it does not curl even when printed on plain paper. In addition, it has good character reproducibility, does not cause a phenomenon such as so-called back-through, which is a phenomenon in which ink is removed from the back of the recording medium and seen from the back, and there is no show-through even immediately after printing. Ink and excellent drying properties can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.

  A dye ink was prepared according to the method described below.

  Each additive such as solvent, pigment, activator, and dispersant shown in Tables 1 and 2 below is dispersed for 2 hours using a paint shaker, and then filtered and membrane deaerated using a hollow fiber membrane. It processed and prepared the inkjet ink (Examples 1-13, Comparative Examples 1-6). Dispersant A (acrylic acid ester copolymer (molecular weight 12,000) copolymerized with methacrylic acid, methyl methacrylate, ethylhexyl methacrylate, and hydroxyethyl acrylate) was used as the dispersant. In the table, S1, S2, S3, and S4 represent S values of the solvents 1 to 4, respectively, and C1 to C4 represent mass fractions (%) of the respective solvents.

SDS: sodium dodecyl sulfate orphine E1010; ethylene oxide (10 mol) adduct of acetylenic diol (manufactured by Nissin Chemical)
<< Inkjet image formation >>
Mounted with a piezo head with a nozzle diameter of 23 μm, 128 nozzles per color, and the same color nozzle density of 90 dpi (dpi represents 1 inch, that is, the number of dots per 2.54 cm), recording density 1440 dpi × 1440 dpi, 1 drop Each of the produced ink-jet inks is set in an on-demand type ink-jet printer set to have a droplet volume per droplet of 6 pl, and further, plain paper (Konica copy paper NR-A100 (manufactured by Konica Minolta Business Technology Co., Ltd.) is used as a recording medium. )) Was set on the paper feed tray, and a solid image of 10 cm × 10 cm was printed with each ink so that the solid images with each ink were adjacent to each other. Samples were prepared in low-speed printing (recording speed of 3 m / min in the sub-scanning direction) mode and high-speed printing (5 m / min in the same mode). Evaluation was performed.

<Evaluation of image recording sample>
(Evaluation of strikethrough resistance)
The back side of the sample printed on the plain paper (Konica copy paper NR-A100) was visually observed and evaluated for see-through resistance 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 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 recognized and is unsuitable for backside printing (evaluation of curl resistance)
About the sample which carried out solid printing with the said area of 10 cm x 10 cm, after printing, it was left for 3 minutes in the environment, the curl was measured, and 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, and quality that poses practical problems (Evaluation of set-off)
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: Clear ink transfer was observed. Vigorous ink transfer was observed (evaluation of duplex printing suitability)
Immediately after the set-off evaluation, 200 sheets of the above-described solid print image evaluated for the set-off were set again on the paper feed tray of the inkjet printer so that the reverse side would be the print surface. Was printed continuously.

  The suitability for double-sided printing was comprehensively determined by checking whether there was a conveyance failure or contamination of the printer conveyance section during or after printing.

A: No conveyance failure or contamination of the printer conveyance unit was observed. B: No conveyance failure was observed, and no contamination of the printer conveyance unit was observed. C: No conveyance failure was observed, and the printer conveyance unit was not recognized. Slight contamination was observed, but it was not a problem for practical use.

D: Conveyance failure occurred during continuous printing, and contamination was observed in the printer transport section E: Conveyance failure occurred frequently during continuous printing, and considerable contamination was observed in the printer transport portion About each inkjet ink of Examples 1-13 and Comparative Examples 1-6, each evaluation result in low-speed printing and high-speed printing was shown in the table | surface.

  It can be seen that the samples according to the present invention of Examples 1 to 13 show good results overall.

Claims (11)

In an inkjet ink containing a colorant and a solvent,
When ΣS defined by the following formulas (1) and (2) was determined for the solvent contained in the inkjet ink, the value was 6 or more and less than 35, and the solvent contained 10% by mass or more of water, An ink-jet ink containing less than 45% by mass.
Formula (1) S = H / M × 1000
H: Total number of hydroxyl groups and amino groups per solvent molecule
M: Molecular weight of solvent Formula (2) ΣS = S ₁ × C ₁ + S ₂ × C ₂ + S ₃ × C ₃ ... + S _n × C _n
S ₁ : S of solvent 1, C ₁ : mass fraction in ink of solvent 1
S _n : S of solvent n, C _n : Mass fraction in ink of solvent n 2. The inkjet ink according to claim 1, wherein a value of ΣS defined by the formula (2) is 6 or more and less than 25. 3. The inkjet ink according to claim 1, wherein the inkjet ink contains a surfactant and the content of the surfactant is less than 1% by mass. The inkjet ink according to claim 3, wherein the content of the surfactant is less than 0.1% by mass. The sum of the content of the solvent whose value of S defined by said Formula (1) is 25 or more and less than 55 is less than 10 mass%, It is any one of Claims 1-4 characterized by the above-mentioned. Inkjet ink. 6. The inkjet ink according to claim 5, wherein the total content of solvents having a value of S defined by the formula (1) of 25 or more and less than 55 is less than 5% by mass. The inkjet ink according to any one of claims 1 to 6, wherein the surface tension is 25 mN / m or more and 35 mN / m or less. The inkjet ink according to any one of claims 1 to 7, further comprising a pigment as a colorant. An inkjet recording method, comprising: discharging the inkjet ink according to any one of claims 1 to 8 by an inkjet head and printing on plain paper. An ink jet recording method comprising: discharging the ink jet ink according to any one of claims 1 to 8 by an ink jet head, and printing at a recording speed of 5 m / min or more in the sub-scanning direction. An ink jet recording method comprising: discharging the ink jet ink according to any one of claims 1 to 8 by an ink jet head, and printing on both surfaces of a recording medium.