JP2007091909A - Yellow ink for inkjet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide yellow ink for inkjet in which the dispersion of an yellow pigment in the ink is highly stable, the agglomeration of the yellow pigment is hard to appear even after the residence for a long period of time, the ink is hard to clog up a printing head when discharged as an ink, the ink enables to achieve a stable image density and a stable printing quality without the lack of a pixel in a character, etc. printed by the ink. <P>SOLUTION: This yellow ink for inkjet comprises a solvent of ≥50 mass% and <90 mass% based on the total mass of the ink, the surface tension of which at 25°C is 25-40 mN/m, the viscosity of which at 25°C is 1-50 mPa s and the vapor pressure of which at 25°C is ≤133 Pa, and water of ≥10 mass% and <45 mass%, PY150 pigment containing a nickel complex and a polymer dispersant. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel inkjet yellow ink.

  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 special paper, there is a problem in that the 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.).

  As for the composition of inkjet ink, it can print 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 appears on the back), feathering Various studies have been made from the viewpoints of no occurrence of image bleeding, rapid penetration into paper, and quick drying.

  As one of the methods, a so-called water-based ink-jet ink having a water content of 50% by mass or more is widely used as an ink-jet ink. An electrophotographic copy paper using such a water-based ink-jet ink is widely used. When recording images on plain paper such as high-quality paper and medium-quality paper, in addition to problems caused by penetrability such as image back-through and feathering, curling and cockling of the recorded plain paper is a major problem. Become.

  In order to solve the above problem, 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 is 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

  In addition, 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 tends to occur at the nozzle portion of the recording head as the ink is dried.

  Further, as a method for improving the curl, an inkjet recording method supplement is 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 the ability to record on both sides, 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 is likely to occur during transportation. there were.

  Further, solvent-based inks that can perform printing at high speed instead of water-based inkjet inks have been 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 high penetrability into plain paper media, resulting in poor character reproducibility and show-through in recording media, and are a major obstacle especially when printing on both sides of plain paper. It was.

  In addition, as a yellow ink used for an aqueous inkjet ink, a dispersion medium is a nonpolar insulating solvent, and pigments exhibiting specific yellow, magenta, cyan, and black colors are soluble in the dispersion medium. An ink that is dispersed in a solution in which a specific resin is dissolved is disclosed (for example, see Patent Document 4).

  A water-based black ink mainly composed of a polymer dispersant, a water-soluble solvent and water and using carbon black, and C.I. I. Aqueous yellow inks using pigments selected from CI Pigment Yellow 17 and 83, and C.I. I. Pigment Red 48: 3, 83 and 122, an aqueous magenta ink using a pigment selected from C.I. I. An aqueous cyan ink using Pigment Blue 15: 3 is disclosed (for example, see Patent Documents 5 and 6).

  Further, regarding the physical properties of the yellow pigment, those specifying a specific wavelength to be absorbed by the ink pigment and those specifying a specific surface tension are disclosed, but all relate to water-based inks (for example, Patent Documents 7 and 8). No reference is made to solvent-rich composition inks.

  However, in these aqueous inkjet ink solvents, the yellow pigment in the ink cannot be kept stably dispersed in the solvent. Therefore, the problem that the yellow pigment particles in the ink are aggregated and easily clogged in the nozzle portion of the recording head has not been solved.

  For this reason, there is disclosed an ink-jet ink that has improved light-emitting properties and decapability at the time of printing, has excellent anti-through-through resistance when printed on plain paper, character quality, and curl characteristics, and an ink-jet recording method using the same. For example, see Patent Documents 9 and 10).

According to this method, a water-insoluble colorant is contained in a dispersion medium containing 50% by mass or more and less than 90% by mass of the solvent with respect to the total mass of the ink and having a water content of 10% by mass or more and less than 45% by mass. It is disclosed that an ink-jet ink can be obtained by dispersing it, having excellent emission stability and decap resistance, excellent character quality of formed images and resistance to show-through, and excellent curl characteristics of printed recording materials. However, the yellow pigment has poor dispersion stability of the yellow pigment. That is, the pigment particle diameter increases with time, the particles in the ink are separated from the liquid, and the head is likely to be clogged when ejected as ink.
JP 10-316915 A JP 9-176538 A JP-A-10-272828 JP-A-5-320551 Japanese Patent Laid-Open No. 10-60330 JP-A-10-120956 JP 2000-290545 A JP 2003-55590 A JP 2005-220296 A Japanese Patent Laid-Open No. 2005-220297

  The present invention has been made in view of the above-mentioned problems, and its purpose is high dispersion stability of yellow pigments used in inkjet yellow inks in inks, and aggregation of yellow pigments is difficult to occur even during long-term liquid stagnation. It is an object of the present invention to provide an inkjet yellow ink that is less likely to be clogged when ejected as ink, and that can achieve a stable print density with no print defects in print quality of characters and the like displayed with yellow ink.

  The above object of the present invention has been achieved by the following constitution.

  50% by mass of a solvent having a surface tension at 25 ° C. of 25 to 40 mN / m, a viscosity at 25 ° C. of 1 to 50 mPa · s, and a vapor pressure at 25 ° C. of 133 Pa or less relative to the total mass of the ink. % PY150 pigment containing a nickel complex, and a polymer dispersant are contained in a solvent having a water content of 10% by weight or more and less than 45% by weight. Yellow ink for inkjet.

  2. 2. The inkjet yellow ink as described in 1 above, wherein the polymer dispersant is a polymer dispersant having a polyoxyalkylate group.

  According to the present invention, the yellow pigment used in the yellow ink for ink jet has high dispersion stability in the ink, and the aggregation of the yellow pigment does not easily occur even when the liquid is stagnated for a long time. Thus, it is possible to provide an inkjet yellow ink that is less likely to occur and that can achieve a stable print density with no image missing in print quality of characters and the like displayed with yellow ink.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above-mentioned problems, the present inventors contain a solvent having a specific surface tension, viscosity and vapor pressure specified in the present invention in an amount of 50% by mass or more and less than 90% by mass with respect to the total mass of the ink. In addition, the ink jet yellow ink using a PY150 yellow pigment containing a nickel complex in a solvent having a water content of 10% by mass or more and less than 45% by mass improves the light emission in the recording head, and makes it possible to produce plain paper. The present inventors have found that an ink jet ink excellent in character quality when printed can be realized, and have reached the present invention.

  Further, it has been found that the dispersibility of the pigment becomes more stable with respect to the dispersion medium system having a weak solvent-rich polarity by using a PY150 yellow pigment containing a nickel complex as the yellow pigment.

  The clear mechanism by which dispersibility becomes more stable is unknown, but it is presumed that it is as follows.

  In the solvent solvent-rich composition, the polarity is not as strong as water, and the non-polar solvent is not as polar as in the case of using a non-polar solvent. It is in a dispersed state. At this time, the polymer dispersant is present in the ink adsorbed on the surface of the yellow pigment, but the steric hindrance can only overcome the intermolecular force between the particles of the yellow pigment with only the polymer chain of the dispersant. The effect is not obtained. For this reason, it is considered that the aggregation of the yellow pigment particles is likely to occur.

  Therefore, when PY150 yellow pigment particles containing a nickel complex are used in a weakly polar ink, the electrostatic obstacle effect between the solvent and the ionization layer of the nickel complex contained in the yellow pigment particles is increased, and the yellow pigment particles It turned out that it becomes difficult to aggregate in the ionosphere around the nickel complex.

  In order to achieve such a phenomenon, it has been found that a PY150 yellow pigment having a nickel complex structure is preferable.

  Details of the present invention will be described below.

〔solvent〕
In the inkjet ink of the present invention (hereinafter also simply referred to as ink), the surface tension at 25 ° C. is 25 to 40 mN / m as a dispersion solvent, the viscosity at 25 ° C. is 1 to 50 mPa · s, and 25 ° C. It is necessary to contain a solvent having a vapor pressure of 133 Pa or less at 50% by mass or more and less than 90% by mass with respect to the total mass of the ink.

  As described above, in the solvent (aqueous solvent) according to the present invention, as one requirement, the surface tension at 25 ° C. is 25 to 40 mN / m, preferably 25 to 32 mN / m. Further, the viscosity at 25 ° C. is one of the characteristics that it is 1 to 50 mPa · s, and preferably 1 to 30 mPa · s. Moreover, although it is one of the characteristics that the vapor pressure in 25 degreeC is 133 Pa or less, Preferably it is 1-67 Pa.

  The solvent (aqueous solvent) that can be used in the present invention is not particularly limited as long as it satisfies all the three liquid properties defined above. For example, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl Ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, Propylene glycol monobutyl ether, dipropylene glycol monomethyl ether , Dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tetrapropylene glycol monomethyl ether, diethylene glycol diethyl ether , Diethylene glycol dibutyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, dipropylene glycol dibutyl ether, tripropylene glycol dibutyl ether, 3-methyl-2,4-pentanediol, diethylene glycol monoethyl ether acetate, 2-methyl- 2,4-penta Diol, 1,5-pentanediol, ethanol, and 2-pyrrolidone.

  Among them, DPGmME (dipropylene glycol monomethyl ether), DPGmEE (dipropylene glycol monoethyl ether), DEGmBE (diethylene glycol monobutyl ether), 2,4-PDO (2-methyl-2,4-pentanediol), EGmBE (ethylene glycol) Monobutyl ether), 1,5-PDO (1,5-pentanediol), EtOH (ethanol), 2-PDN (2-pyrrolidone), and DEG (diethylene glycol) are preferred.

  Each characteristic value of the aqueous solvent specified in the present invention can be determined according to each data described in “New Edition Solvent Pocket Book” edited by Organic Synthetic Chemistry Association, Ohm Co. (1994), or a known measurement method. .

  In the ink of the present invention, it is one of the characteristics that water is contained in an amount of 10% by mass or more and less than 45% by mass with respect to the total mass of the ink, preferably 10% by mass or more and less than 30% by mass. is there. By setting the water content in the ink within the range specified in the present invention, both the ink permeation speed and the curl characteristics can be set to optimum conditions.

[Yellow pigment]
The yellow pigment can be used without particular limitation as long as it is a PY150 yellow pigment containing a nickel complex. For example, as a commercially available PY150 yellow pigment, Pigment Yellow Y-5688, E4GN-GT, E4GN, and BASF Heliofast Yellow 4G manufactured by LANXESS are applicable.

(Polymer dispersant)
The pigment used in the present invention is used after being dispersed by a disperser using a polymer dispersant. In addition, the steric hindrance effect, which was not effective with ordinary dispersants, is that when a polymer dispersant having a polyoxyalkylate group is used, the bond between the functional group and the nickel complex is strengthened, which affects the steric hindrance effect. It was found that the dispersion high molecular weight increases, so that the stability during dispersion is further increased.

As a polymer dispersant having a polyoxyalkylate group,
Copolymer obtained by polymerizing methacrylic acid, methyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl acrylate (mass ratio = 40/20/10/30), latex having a weight average molecular weight of 12,000: Nipol SX-1706 (acrylic acid ester copolymer, soap-free latex, manufactured by Nippon Zeon),
Acrylic-styrene copolymer polymer: DispersBYK (by Big Chemie),
Acrylic-styrene copolymer polymer: efka4570 (manufactured by Fuka Additives Inc.) and the like are preferably used.

  The pigment used in the present invention is preferably used after being dispersed by a disperser together with a polymer dispersant and other additives necessary for various desired purposes. As the disperser, a conventionally known ball mill, vibration mill, sand mill, line mill, high-pressure homogenizer, or the like can be used.

  The average particle diameter of the pigment dispersion used in the ink of the present invention is preferably 50 to 200 nm. When the average particle size of the pigment dispersion exceeds 200 nm, the dispersion becomes unstable. Further, even when the average particle size of the pigment dispersion is less than 50 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 measured 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.

〔Additive〕
In the ink of the present invention, a surfactant can 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.

  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, Alkyl benzene 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 ink droplets after ink ejection into plain paper, 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.

  In the 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, particularly 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 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 the ink of the present invention having the above-described structure, the surface tension of the ink is preferably 25 to 40 mN / m at 25 ° C., more preferably 25 to 35 mN / m, and further preferably 30 to 35 mN / m. It is. The ink viscosity is preferably 1 to 40 mPa · s at 25 ° C., more preferably 5 to 40 mPa · s, and further preferably 5 to 15 mPa · s. 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).

  In the image forming 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 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. 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, a thermal type) Any discharge method such as an ink jet type or a bubble jet (registered trademark) type may be used.

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

  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 with a shuttle head type recording head using a line head type recording head. It is possible to achieve extremely good isot shape (roundness) and printing accuracy when landing on plain paper. In particular, in the recording method using the ink of the present invention, image printing can be performed on both sides of plain paper. 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.

  The plain paper used in the 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 improving the penetration of the ink of the present invention and the fixability of the colorant. The water-soluble polyvalent metal salt is not particularly limited, and examples thereof include aluminum, calcium, magnesium, zinc, iron, strontium, barium, nickel, copper, scandium, gallium, indium, titanium, zirconium, tin, and lead. 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.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

Example 1
<< Preparation of Inks 101-104 of the Present Invention >>
After mixing PY150 yellow pigment, solvent (aqueous solvent), water, and polymer dispersant in the combinations shown in Table 1, the mixture was sealed in a glass bottle with 200 g of zirconia beads having a diameter of 1.0 mm, and 2 in a paint shaker. After preparing each pigment dispersion by time dispersion treatment, zirconia beads were removed, and this liquid was subjected to filtration and membrane deaeration treatment using a hollow fiber membrane to prepare inks 101 to 104. The mixing ratio of the aqueous solvent, water, and polymer dispersant is as follows.

Pigment (PY150 yellow pigment) 4.0 parts Aqueous solvent (Tripropylene glycol monomethyl ether) 69.5 parts Water 25.0 parts Polymer dispersant (Tripropylene glycol monomethyl containing 33% by mass of acrylic-styrene copolymer polymer) Ether solution) 1.5 parts The surface tension of the solvent (tripropylene glycol monomethyl ether) at 25 ° C. is 30 mN / m, the viscosity at 25 ° C. is 6.2 mPa · s, and the vapor pressure at 25 ° C. is 4 Pa. In addition, four types of PY150 yellow pigments were used and are shown in Table 1.

<< Preparation of Inks 105 and 106 of Comparative Examples >>
Inks 105 and 106 were prepared in the same manner as the preparation of the ink 101 with the following combinations of materials.

Pigment (PY150 yellow pigment) 4.0 parts Aqueous solvent (Tripropylene glycol monomethyl ether) 69.5 parts Water 25.0 parts Low molecular weight dispersant (see Table 1) 1.5 parts << Ink of Comparative Examples 107 to 110 Preparation
Inks 107 to 110 were prepared in the same manner as the preparation of the ink 101 with the following combinations of materials.

Pigment (see Table 1) 4.0 parts Aqueous solvent (Tripropylene glycol monomethyl ether) 69.5 parts Water 25.0 parts Polymer dispersant (acryl-styrene copolymer) 1.5 parts << Ink 111 of Comparative Example Preparation of ~ 114
Inks 111 to 114 were prepared in the same manner as the preparation of ink 101 using the following combination of materials.

Pigment (see Table 1) 4.0 parts Aqueous solvent (Tripropylene glycol monomethyl ether) 69.5 parts Water 25.0 parts Polymer dispersant (styrene-maleic anhydride copolymer polymer) 1.5 parts << Comparative Example Preparation of inks 115-119 of
Inks 115 to 119 were prepared in the same manner as the preparation of ink 101 using the following combinations of materials.

Pigment (see Table 1) 4.0 parts Aqueous solvent (Tripropylene glycol monomethyl ether) 69.5 parts Water 25.0 parts Polymer dispersant (polyvinyl alcohol) 1.5 parts << Measurement of ink material and ink characteristic values >>
(Measurement of average particle size of pigment dispersion)
At 25 ° C., the Brownian motion of the particles in the dispersion was detected by a dynamic light scattering method, the particle size was calculated, and the average value was obtained. The measuring instrument used was a Zetasizer manufactured by Malvern Instruments.

[Measurement of solvent surface tension]
The dynamic surface tension was measured at 25 ° C. using an automatic dynamic surface tension meter SV-100 manufactured by Kyowa Interface Science Co., Ltd.

[Measurement of solvent and ink viscosity]
The measurement was performed at 25 ° C. using a vibration type viscometer utilizing the fact that the amplitude of the minute vibration of the detector changes depending on the viscosity of the measurement liquid. SV-100 manufactured by A & D Co., Ltd. was used as a measuring instrument.

<Evaluation of ink>
(Evaluation of light emission)
The pigment inks 101 to 119 prepared above were emitted using a shear mode piezo-type recording head having a nozzle diameter of 25 μm, a discharge ink droplet amount of 4 pl, a driving frequency of 10 kHz, and a nozzle number of 512, and the emission property was evaluated. The drive voltage was adjusted so that the discharge speed was 6 m / s.

  In the emission, under the environment of 25 ° C. and 50% relative humidity, 500 ml of each ink was continuously ejected, the bending that occurred until the ink ran out, the missing radiation was visually observed, and the emission property was evaluated according to the following evaluation criteria. .

◎: All nozzles emitted stably to the end ○: At the end, 1-20 nozzles were bent and missing occurred △: Finally, 21-40 nozzles were bent, and missing occurred ×: Final Bending with 41 or more nozzles at the same time resulted in a lack of fire [Evaluation of character quality]
Using a shuttle head type piezo-type recording head having a nozzle diameter of 25 μm and a nozzle number of 512, the recording resolution is 1440 × 1440 dpi (in the present invention, dpi represents the number of dots per 2.54 cm), ink Using the ink prepared above under the conditions of an adhesion amount of 10 ml / m ² and an image size of 280 × 200 mm, a solid image and a resolution of 1440 × 1440 dpi on one side of first class plain paper manufactured by Konica Minolta Business Technology, Inc., A4 size. The character images of hiragana “A, I, U, E, O” were printed in 3 and 4 points Mincho.

  The character images of the hiragana characters “A, I, U, E, O” were visually observed with the 3-point and 4-point Mincho bodies created above, and the character quality was evaluated according to the following evaluation criteria.

◎: 3-point character image is clearly recorded in detail ○: Even 3-point character image can be read △: Crushing is seen in part of 3-point character image, but 4-point character image X: Crush is observed in a part of a 4-point character image. XX: Clear crush is seen in a 4-point character image, and is difficult to read. Ink material, ink characteristic value, and emission Table 1 shows the evaluation results of the character quality.

  As can be seen from Table 1, the aqueous solvent satisfying the conditions defined by the present invention in terms of surface tension and viscosity and the yellow pigment ink defined by the present invention have better ink ejection properties than the comparative examples. It can be seen that an image recorded on plain paper using is excellent in character quality.

  In particular, the combination of the yellow pigment PY150 and the polymer dispersant was confirmed to be effective in the above-mentioned solvent-rich ink. Combinations of low molecular dispersants and PY-150 yellow pigments described in other comparative examples, polymer dispersants other than dispersants having polyoxyalkylate groups (for example, acrylic styrene copolymers) and PY It was found that a combination with a yellow pigment other than -150 yellow pigment and PY150 yellow pigment aggregates in the ink and causes clogging of the head.

Example 2
Inks 201 to 219 were prepared in the same manner as in Example 1 except that the solvent (tripropylene glycol monomethyl ether) used in Example 1 was replaced with 2-methyl-2,4-pentanediol having a low surface tension. Measured and evaluated. The results are shown in Table 2.

  The solvent (2-methyl-2,4-pentanediol) has a surface tension at 25 ° C. of 26 mN / m, a viscosity at 25 ° C. of 31 mPa · s, and a vapor pressure at 25 ° C. of 2.7 Pa. there were.

  As is clear from Table 2, even when a solvent having a low surface tension is used, the solvent satisfying the conditions defined by the present invention in terms of surface tension and viscosity, and the yellow pigment ink defined by the present invention are compared with the comparative examples. It can be seen that the ink output is good, and the image recorded on plain paper using this ink is excellent in character quality.

Example 3
Inks 301 to 330 were prepared in the same manner as in Example 1 except that the solvent (tripropylene glycol monomethyl ether) used in Example 1 was replaced with diethylene glycol having a high surface tension, and measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 3.

  The surface tension of the solvent (diethylene glycol) at 25 ° C. was 48 mN / m, the viscosity at 25 ° C. was 30 mPa · s, and the vapor pressure at 25 ° C. was less than 1.3 Pa.

  As is apparent from Table 3, even when a solvent having a high surface tension is used, the solvent satisfying the conditions specified by the present invention in terms of surface tension and viscosity, and the yellow pigment ink defined by the present invention, It can be seen that the ink output is good, and the image recorded on plain paper using this ink is excellent in character quality.

Claims (2)

A solvent having a surface tension at 25 ° C. of 25 to 40 mN / m, a viscosity at 25 ° C. of 1 to 50 mPa · s, and a vapor pressure at 25 ° C. of 133 Pa or less is 50% by mass or more based on the total mass of the ink. And a PY150 pigment containing a nickel complex and a polymer dispersant in a solvent containing less than 90% by mass and having a water content of 10% by mass or more and less than 45% by mass. Yellow ink. The yellow ink for inkjet according to claim 1, wherein the polymer dispersant is a polymer dispersant having a polyoxyalkylate group.