JP2007246866A - Inkjet ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inkjet ink for regular paper which satisfies both of the prevention of curling and the prevention of strike-through and is also excellent in storage stability (dispersion stability of ink). <P>SOLUTION: The inkjet ink is characterized by containing a pigment, a polymer, water and a water-soluble organic solvent and pigment wherein the content of the water is from 10 mass% or more to less than 50 mass% based on the total ink mass, the SP value of the water soluble organic solvent that is most largely included among the water-soluble organic solvents is from 16.5 or more to less than 24.6, further the content of the water-soluble solvent having the SP value of from 16.5 or more to less than 24.6 is from 30 mass% or more to 90 mass% or less based on the total ink mass. The inkjet ink is further characterized by containing 0.01 ppm-50 ppm of Sr<SP>2+</SP>ion based on the total ink. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet ink, and more particularly to an inkjet ink suitable for an inkjet recording method capable of high-quality double-sided printing.

  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, and special printing such as color filters. In particular, ink jet recording devices that emit and control fine dots, ink with improved color reproduction range, durability, and emission suitability, ink absorbency, colorant color development, surface gloss, etc. are dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper.

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

  On the other hand, in the office, there is an increasing need for a system 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.).

  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), feathering Various studies have been made from the viewpoints of no occurrence of image bleeding, rapid penetration into paper, and quick drying.

  In particular, for inkjet recording devices intended for double-sided printing, when double-sided printing is performed on plain paper, if the back-through on printing is large, the back-through image overlaps with the printed content on the back, making it very difficult to see. End up.

  On the other hand, in the case of a printing form with high-speed printing in mind, the printed material is overlaid immediately after printing, and the ink of the lower paper is reflected on the back surface of the upper paper, so the surface dryness of the printed material is required. At the same time, prints without curling and cockling were required to prevent paper jams during high-speed transport.

  As a means for improving the surface drying property of the printed matter, a method of providing a drying means has been disclosed. For example, by drying with infrared rays, even a slow-drying ink can be dried in a short time. It is disclosed that accurate printing can be achieved (see Patent Document 1). However, the above method has a problem of curling due to drying. On the other hand, a method of providing a mechanism for correcting a curl caused by drying has been disclosed (see Patent Documents 2 and 3). However, these methods require time to correct curl and increase the number of devices, so they are useful on large devices and industrial lines, but they are not suitable for office specifications. In addition, the cost burden is large.

  On the other hand, as a means for improving the surface drying property of the printed matter, a method of giving the ink surface drying property has been devised. As a method for achieving both the emission stability and the surface drying property, a method for improving the surface drying property by increasing the permeability of the ink into the paper and realizing high-speed printing is disclosed. For example, an ink that defines a wetting time by the Bristow method is disclosed (see Patent Document 4). However, when ink with high penetrability is used, there is a problem that the ink coloring material easily penetrates into the inside of the paper, the back-through becomes large, and the printing quality is deteriorated when printing on both sides of the paper.

  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 also have high penetrability inside the paper, causing back-through, which has been a major obstacle especially when printing on both sides of plain paper.

Even with the above technologies, curl and strikethrough are not compatible.
JP 63-252772 A JP 2001-301151 A JP 2002-187264 A JP 10-316915 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an inkjet ink for plain paper that has both curling prevention and prevention of back-through prevention and excellent storage stability (ink dispersion stability). There is to do.

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

1. A pigment, a polymer dispersant, water, a water-soluble organic solvent and a pigment, wherein the water content is 10% by mass or more and less than 50% by mass of the total ink mass, Among them, the SP value of the most water-soluble organic solvent is 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having the SP value of 16.5 or more and less than 24.6 is the total ink mass. An ink-jet ink characterized by containing Sr ²⁺ ions in an amount of 0.01 ppm to 50 ppm of the total ink.

2. A pigment, a polymer dispersant, water, a water-soluble organic solvent and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass. The SP value of the most water-soluble organic solvent contained is from 16.5 to less than 24.6, and the content of the water-soluble organic solvent having the SP value of from 16.5 to less than 24.6 is the total ink mass. An ink-jet ink comprising 30% by mass or more and less than 90% by mass and containing 0.05 ppm to 10 ppm of Sr ²⁺ ions in the total ink.

  ADVANTAGE OF THE INVENTION According to this invention, the inkjet ink for plain papers which is compatible in curl prevention and prevention of back-through and excellent in storage stability (ink dispersion stability) can be provided.

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

  A pigment, a polymer dispersant, water, a water-soluble organic solvent and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass. The SP value of the most water-soluble organic solvent contained is from 16.5 to less than 24.6, and the content of the water-soluble organic solvent having the SP value of from 16.5 to less than 24.6 is the total ink mass. In the ink jet ink of 30% by mass or more and less than 90% by mass, the solvent is hydrophobic, so that the interaction with cellulose hardly occurs and curling does not occur. On the other hand, the ink contains water. Since it is a solvent that is compatible with water, a water-based pigment can be used for dispersion, and therefore no show-through occurs.

  As the amount of water contained in the ink increases, the show-through tends to decrease. However, if a predetermined amount or more of water is included, curling occurs even when the water-soluble organic solvent is contained at 30% by mass or more. . For this reason, the amount of water in the ink is 10% by mass or more and less than 50%, and a preferable range is 20% by mass or more and less than 45%, in order to achieve both prevention of curling and prevention of back-through.

  The water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 in the ink tends to have a higher curling prevention effect as the content is higher. To obtain the effect, it is necessary to include 30% by mass or more. It is preferable to contain 50 mass% or more. Regarding the upper limit of the content of the water-soluble organic solvent, it cannot be contained in an amount of 90% by mass or more because the condition for the content of water is satisfied. preferable.

  Further, since a small amount of Sr ions is contained in the ink-jet ink without curling and see-through, the dispersion stability of the ink can be improved without deteriorating the characteristics of the ink.

  The solvent of the ink according to the present invention contains a large amount of an organic solvent, so that the dispersing agent is difficult to spread and it is difficult to obtain a three-dimensional exclusion effect. In addition, since the dielectric constant of the ink solvent is low, it is difficult to stabilize the charge. .

The present inventors have found that the storage stability of the ink can be improved by containing 0.01 ppm to 50 ppm of Sr ²⁺ ions in the solvent of the ink according to the present invention.

This is because the Sr ²⁺ ions take a structure like a loose bridge between the dispersants, and the cross-linked Sr ²⁺ repels each other, so that the dispersion of the dispersant is stable even in the solvent in the present invention. I think so. Furthermore, the fact that a repulsive force can be obtained with a slight charge is considered to contribute to the improvement of the stability of the dispersant.

However, when a large amount of Sr ²⁺ is present, the dispersion stability is impaired due to the influence of electric charges. The present inventors have found that an ink with high dispersion stability can be obtained by controlling the amount of Sr ²⁺ ions in the range of 0.01 ppm to 50 ppm in the system of the present invention.

  JP-A-8-311376 discloses a method for defining the amount of strontium in an ink as an ink-jet ink technique that regulates the strontium concentration of the ink. In this form, the ink solvent satisfying the requirements of the present invention is not used. Therefore, a system that is limited to pigments in a solvent that meets the requirements of the present invention and the system in which the patent is implemented are quite different and are therefore not related to the effect of the present invention.

  Hereinafter, the present invention will be described in detail.

  First, it is assumed that the ink of the present invention is discharged onto plain paper. The plain paper in the present invention will be described. Examples of the plain paper in the present invention include those generally called high-quality paper, neutral paper, and copy paper. When a recording sheet or paper is used in the text, it means plain paper.

  The aqueous inkjet ink of the present invention contains at least water, a water-soluble organic solvent, and a pigment. Here, the water-soluble organic solvent is not particularly limited as long as it can be mixed with water. Two or more water-soluble organic solvents can be used in combination. Of the water-soluble organic solvents, the most water-soluble organic solvent has an SP value of 16.5 or more and less than 24.6, and further contains a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 The solvent composition is preferably 30% by mass or more of the total ink mass. Since this solvent composition contains a large amount of a water-soluble organic solvent having a higher hydrophobicity than water, the solubility of the entire ink is high and curling does not occur.

  The solvent solubility parameter (SP value) in the present invention is a value represented by the square root of the molecular cohesive energy. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1974). The unit is (MPa) 1/2, and refers to the value at 25 ° C.

  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 the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6, conventionally known various water-soluble organic solvents can be used in combination.

  Examples of water-soluble organic solvents preferably used as the solvent used in combination include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexane). Hexanol, 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, 1,3-propanediol, 1,4-butanediol, 1,5-pentanedio , 1,2-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol, etc.), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine) , Morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocyclic rings (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidone, etc.), sulfoxides For example, dimethyl sulfoxide, etc.), sulfones (e.g., sulfolane), urea, acetonitrile, and acetone.

  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.

  As the hue of the pigment used in the present invention, for example, yellow, magenta, cyan, black, blue, green, and red are preferably used, and yellow, magenta, cyan, and black colorants are particularly preferable.

  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.

  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.

  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.

Furthermore, as a feature of the ink of the present invention, it contains 0.01 ppm to 50 ppm of Sr ²⁺ ions. If Sr ²⁺ ions are contained in an amount exceeding 50 ppm, the electrical balance in the system will be lost and the dispersion stability of the ink will be deteriorated. If it is less than 0.01 ppm, the effect of the present invention cannot be obtained. More preferably, it is in the range of 0.05 ppm to 10 ppm.

As the Sr ²⁺ ion source, any salt containing strontium soluble in water may be used. Examples thereof include SrBr ₂ , SrI ₂ , SrCl ₂ , Sr (NO ₃ ) ₂ , strontium borate, and other organic salts having a solubility of 0.01 ppm or more at the pH of the ink. It is preferable to use a strontium salt having high solubility in order to prevent clogging of the head.

  It is preferable to add a salt containing strontium soluble in water before dispersion or at the same time when the dispersion is diluted, because it is easy in work and does not cause inadvertent aggregation.

For Sr ^{2+ in} the ink, for example, the ink is centrifuged to separate a supernatant component and a precipitation component, and the amount of Sr ²⁺ ions is measured by measuring the supernatant component by any known method. Can do.

As a method for adjusting the Sr ²⁺ concentration, Sr may be contained as an impurity such as a pigment or a dispersant, and is preferably added and adjusted to a dispersion or ink treated with a cation exchange resin.

  In the present invention, the polymer dispersant refers to a compound having a polymer component having a molecular weight of 5000 or more and 200000 or less. The polymer dispersant is selected from styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid and fumaric acid derivatives. Examples thereof include a block copolymer comprising at least one kind of monomer, a random copolymer and salts thereof, polyoxyalkylene, and polyoxyalkylene alkyl ether.

In the present invention, the polymer dispersant preferably has a highly polar group such as an ether bond, an ester bond, a carbonyl group, or a hydroxyl group in the molecule during dispersion. By using a dispersant having a highly polar group such as an ether bond, an ester bond, a carbonyl group, an unsaturated carbon, or a hydroxyl group in the molecule, the effect of adding Sr ²⁺ to the ink appears sufficiently and good dispersibility Indicates.

  In the case of an acidic polymer dispersant, it is preferably added after neutralization with a neutralizing base. Here, the neutralizing base is not particularly limited, but is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine.

  Moreover, in this invention, it is preferable that the addition amount of a polymer dispersing agent is 10-100 mass% with respect to a pigment.

  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 image forming method using the ink-jet ink of the present invention, for example, an ink-jet print is 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 the ink-jet ink. It is done.

  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 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. Recording is performed on plain paper by discharging from a piezo ink jet recording head of a line head type having a nozzle 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 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, the inkjet recording system according to the ink of the present invention is intended to print an image on 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 ink jet recording method according to 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. In the present invention, as the pulp material used for plain paper, mechanical pulp or recycled paper recycled pulp may be used in combination, and there is no problem even if these are used as the main material.

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

  Further, in the present invention, as fillers internally added to plain paper, for example, finely divided silicic acid, aluminum silicate, diatomaceous earth, kaolin, kaolinite, halloysite, nacrite, dickite, pyrophyllite, sericite, titanium dioxide, bentonite, etc. Is mentioned.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. In addition, unless otherwise indicated, "part" in an Example shows a "mass part".

Example 1
<< Preparation of ink (ink dispersion) >>
In the combinations shown in Table 1, the pigment, the aqueous solvent, water, and the resin were mixed, then mixed with 50 g of an H-type ion exchange resin and stirred for 1 hour, and only the ion exchange resin was removed by filtration. Thereafter, strontium nitrate is added to the filtered mixture at the ratio shown in Table 1, and 200 g of zirconia beads having a diameter of 1 mm are placed in a glass bottle and tightly sealed, and each pigment is dispersed by a paint shaker for 2 hours. After preparing the liquid, the zirconia beads were removed, and the remaining liquid was filtered and subjected to membrane deaeration treatment using a hollow fiber membrane to prepare inks 1 to 13.

  In addition, all the numerical values in Table 1 indicate parts by mass.

  The aqueous solvent and resin used above are described below.

<Resin (polymer compound)>
Resin 1: Copolymer obtained by polymerizing methacrylic acid, methyl methacrylate, 2-ethylhexyl methacrylate and hydroxyethyl acrylate (mass ratio = 40/20/10/30), average weight molecular weight = 12,000
Resin 2: The terminal of the copolymer obtained by polymerizing oxyethylene and oxypropylene (mass ratio = 70/30) is laurylated. Average weight molecular weight = 20,000
Resin 3: Commercially available dispersant: EFKA4570 (acrylic polymer compound manufactured by EFKA)
<Solvent (aqueous solvent)>
DPGME: Dipropylene glycol monomethyl ether (SP value: 21.3)
TPGME: Tripropylene glycol monomethyl ether (SP value: 20.4)
EG: ethylene glycol (SP value: 32.2)
<Sr ²⁺ ion content of ink>
About each produced said ink 1-13, it centrifuged with the centrifugal ultrafiltration apparatus. As the filter, type NMWL10000 was used, and the centrifugation conditions were 2500 G × 60 minutes. The filtrate was analyzed by ICP mass spectrometry to measure the amount of Sr ²⁺ ions in the ink. The results are shown in Table 1.

<Inkjet image recording>
The prepared ink was used in a black cartridge of a Hewlett-Packard printer HP-PSC1610. A 100% black solid image produced by Photoshop 7.0 was printed on one side of A4 size Konica Minolta Business Technology's first class plain paper, and image samples 1-13 for each ink 1-13. Was made.

[Evaluation of curl]
Each sample with the solid image printed thereon was allowed to stand for 1 week in an environment of 23 ° C. and 55% RH, and then the curl was evaluated. A state in which the end portion having a height of 2 mm or more did not float and no occurrence of cockling was observed.

  For each image, the curl was evaluated by the above method, but all the image samples using the inks 1 to 10 showed a good result, and there was no significant difference between the image samples. On the other hand, any of the inks 11, 12, and 13 could not be curled.

[Evaluation of through-hole resistance]
For each of the images 1 to 13 formed above, the density of the image portion and the non-image portion on the recording print surface (referred to as A surface) and the back surface (referred to as B surface) was measured, and the back-through density ratio was measured according to the following equation. In accordance with the following evaluation criteria, the resistance to back-through was evaluated.

Back-through density ratio = (B-side image density−B-side unprinted portion density) / (A-side image density−A-side unprinted portion density) × 100 (%)
A state where the back-through density ratio was less than 8% was regarded as a good state.

  For each image, the strikethrough resistance was evaluated by the above-described method, but the result of each ink was in a good state, and there was no significant difference between the images.

[Evaluation of ink dispersion stability (storage stability)]
For each of the inks 1 to 13, the particle size of the pigment in the ink after 3 days of dispersion and the viscosity of the ink were measured. Further, each ink was stored at 60 ° C. for 3 weeks, and the particle size and viscosity were measured again, and evaluated according to the following criteria.
A: Variation in either particle size or viscosity is less than 5%.
○: The variation of either the particle size or the viscosity is 5% or more and less than 10%.
X: The variation of either the particle size or the viscosity is 10% or more and less than 15%.
XX: The fluctuation of either particle size or viscosity is 15% or more. The viscosity is measured with a vibration viscometer, Viscometer VM-1G (made by Nikkato), and the particle size is measured with a Zetasizer Nano S (made by Malvern). Went.

  The results are shown in Table 1.

  In addition, all the numerical values in a table | surface show a mass part.

  As is apparent from Table 1, the ink of the present invention has extremely excellent resistance to see-through, high printing density, high ink dispersion stability (storage stability), and no problem with curling or surface drying. It turns out that it is ink. The ink having the object effect of the present invention can be provided.

Claims (2)

A pigment, a polymer dispersant, water, a water-soluble organic solvent and a pigment, wherein the water content is 10% by mass or more and less than 50% by mass of the total ink mass, Among them, the SP value of the most water-soluble organic solvent is 16.5 or more and less than 24.6, and the content of the water-soluble organic solvent having the SP value of 16.5 or more and less than 24.6 is the total ink mass. An ink-jet ink characterized by containing Sr ²⁺ ions in an amount of 0.01 ppm to 50 ppm of the total ink. A pigment, a polymer dispersant, water, a water-soluble organic solvent and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink mass. The SP value of the most water-soluble organic solvent contained is from 16.5 to less than 24.6, and the content of the water-soluble organic solvent having the SP value of from 16.5 to less than 24.6 is the total ink mass. An ink-jet ink comprising 30% by mass or more and less than 90% by mass and containing 0.05 ppm to 10 ppm of Sr ²⁺ ions in the total ink.