JP7325204B2 - Ink set and inkjet recording method - Google Patents

Description

The present invention relates to an ink set of dark color ink and light color ink, and an ink jet recording method using the ink set.

An inkjet recording method using an inkjet printer is a method of printing by ejecting small droplets of ink from a printer and attaching the droplets to a recording medium such as paper. Since this method is easy to reduce the size and increase the speed, it has rapidly spread in recent years, and its application for industrial use is also progressing.

When forming a color image by an inkjet recording method, it is common to use at least four color inks of black, cyan, magenta, and yellow as an ink set.
However, when expressing a light-colored image (in other words, an image with a low colorant density) using these four colors, it is necessary to reduce the amount of ink applied. In order to reduce the amount of ink applied, it is necessary to reduce the amount of ink droplets ejected. As a result, a grainy feeling is given to light-colored images, which poses a serious problem that high-quality images cannot be expressed.
One way to solve this problem is to use normal black, cyan, magenta, and yellow dark inks (regular inks with high colorant concentrations), plus light black, light cyan, and light magenta. Ink jet printers have been developed that are loaded with ink sets having light colored inks such as , and light yellow. A light-colored ink means an ink having a hue similar to that of a normal dark-colored ink and having a lower colorant concentration. By using light-colored ink when printing light-colored images, it is not necessary to reduce the amount of ink droplets ejected. Therefore, it is possible to express a high-quality color image without graininess.

Japanese Patent No. 5279255 Japanese Patent No. 5062246 Japanese Patent No. 4232202

However, when an ink set of dark and light inks is used to represent all images from light colors to dark colors, there are image areas where both the light color ink and the dark color ink overlap. In such image areas, "bleeding" easily occurs between the colors of the dark and light inks, and this poses a new problem. Such intercolor bleed significantly degrades image quality. For this reason, there is a strong demand from the market for an ink set of dark-colored ink and light-colored ink that does not cause bleeding.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ink set capable of suppressing color bleeding between dark and light color inks.

The present inventors have made intensive studies to solve the above problems, and found that the above problems can be solved by an ink set in which the static surface tension of the dark-colored ink and the light-colored ink and the difference between them are within a specific range. and completed the present invention. That is, the present invention relates to the following [1] to [11].

[1]
An ink set for inkjet recording comprising dark-colored inks and light-colored inks having different colorant contents in the total mass of the inks, wherein the static surface tensions of the dark-colored inks and the light-colored inks are both 27 mN/m. and the value obtained by subtracting the static surface tension of the light-colored ink from the static surface tension of the dark-colored ink is within ±4 mN/m.
[2]
The ink set according to [1] above, wherein both the dark-colored ink and the light-colored ink contain a water-insoluble colorant as a colorant.
[3]
The ink set according to [2] above, wherein the water-insoluble colorant is a pigment.
[4]
The ink set according to [1] above, wherein at least one of the dark-colored ink and the light-colored ink contains a surfactant selected from silicone-based surfactants and fluorine-based surfactants.
[5]
The ink set according to [4] above, wherein both the dark-colored ink and the light-colored ink contain surfactants selected from silicone surfactants and fluorosurfactants.
[6]
The ink set according to any one of [1] to [5] above, further containing an organic solvent.
[7]
Inkjet recording in which droplets of each ink of the ink set according to any one of [1] to [6] are ejected from an inkjet printer according to a recording signal and adhered to a recording medium to perform recording. Method.
[8]
The inkjet recording method according to the above [7], wherein the recording medium is a recording medium that hardly absorbs ink or that does not absorb ink.
[9]
A recording medium to which each ink of the ink set according to any one of [1] to [6] is adhered.
[10]
An inkjet printer comprising a container containing each ink of the ink set according to any one of [1] to [6] above.
[11]
A method for suppressing inter-color bleeding between dark-colored inks and light-colored inks, using the ink set according to any one of [1] to [6] above.

According to the present invention, it is possible to provide an ink set capable of suppressing color bleeding between dark and light color inks.

As used herein, "C.I." is an abbreviation for Color Index. In addition, in this specification, "%" and "parts" numbers are expressed on a mass basis unless otherwise specified.
Further, in this specification, when there is no need to distinguish between dark-colored ink and light-colored ink, the term "ink" may be simply used to include both.
Each of the above ink sets is a water-based ink set consisting of water-based dark-colored ink and light-colored ink.

[Dark Ink]
The total content of colorants contained in the dark ink is usually 3% to 7%, preferably 3% to 6%, more preferably 3.5% to 5.5%.
With such a content, it is possible to improve both the color density of the recorded image and the ejection property.

[Light color ink]
The total content of the colorant contained in the light-colored ink is usually 0.1% to 2.5%, preferably 0.5% to 2%, more preferably 0.7% to 1.5%, and even more preferably 0.9% to 1.3%.
With such a content, light-colored recorded images can be expressed without graininess.

[Static surface tension]
The static surface tensions of the dark-colored ink and the light-colored ink are both 27 mN/m or less. With such a range, it is possible to perform recording on, for example, non-ink-absorbing media and poorly-ink-absorbing media that do not have an ink-receiving layer, in the same manner as recording media that have an ink-receiving layer. can.
Further, the value obtained by subtracting the static surface tension of light-colored ink from the static surface tension of dark-colored ink is preferably within ±4 mN/m. By setting the static surface tension to such a value, it is possible to suppress bleeding between dark and light color inks even when recording on an ink non-absorbing medium or an ink hardly absorbing medium. In this specification, the numerical value obtained by rounding off the first decimal place in the surface tension measurement value is adopted as the surface tension value.
A surfactant can be used to adjust the static surface tension. Among them, surfactants selected from silicone-based surfactants and fluorine-based surfactants are preferred. By using these surfactants, the range of static surface tension of each ink can be adjusted to the above range.

Examples of silicone-based surfactants include polyether-modified siloxane and polyether-modified polydimethylsiloxane, and specific examples include BYK-306, BYK-307, BYK-333, BYK-341, and BYK-345. , BYK-346, BYK-347, BYK-348, BYK-349, BYK-3455 (manufactured by BYK Chemie), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (manufactured by Shin-Etsu Chemical Co., Ltd.), etc. is mentioned.

Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide-imparted products, and perfluoroalkyl ether groups. Examples include polyoxy chain ether polymer compounds having chains, and specific examples include Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300 (manufactured by DuPont); Capstone FS. -30, FS-31, FS-3100 (manufactured by Chemours); PF-151N, PF-154N (manufactured by Omnova); F-114, F-410, F-444, EXP. TF-2066, EXP. TF-2148, EXP. TF-2149, F-430, F-477, F-552, F-553, F-554, F-555, F-556, F-557, F-558. F-559, F-561, F-562, R-40, R-41, RS-72-K, RS-75, RS-76-E, RS-76-NS, RS-77, EXP. TF-1540, EXP. TF-1760 (manufactured by DIC Corporation); BYK-340, BYK-3440, BYK-3441 and the like (manufactured by BYK-Chemie).

[Coloring agent]
The colorant contained in each ink of the ink set is not particularly limited, and known dyes, pigments, and the like can be used as necessary. Among them, water-insoluble colorants are preferred, and pigments are more preferred, from the viewpoint of image fastness such as light resistance and water resistance of recorded images.

Carbon black such as furnace black, lamp black, acetylene black, and channel black is preferable as the black colorant. Specific examples of carbon black include Raven 760 ULTRA, Raven 780 ULTRA, Raven 790 ULTRA, Raven 1060 ULTRA, Raven 1080 ULTRA, Raven 1170, Raven 1190 ULTRA II, Raven 1200, Rav en 1250, Raven 1255, Raven 1500, Raven 2000, Raven 2500U LTRA, Raven 3500, Raven 5000 ULTRA II, Raven 5250, Raven 5750, Raven 7000 (manufactured by Columbia Carbon); Monarch 700, Monarch 800, Monarch 880, Monarch 900, M Onarch 1000, Monarch 1100, Monarch 1300 , Monarch 1400, Regal 1330R, Regal 1400R, Regal 1660R, Mogul L (manufactured by Cabot); Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Spec Ial Black 4, Spec Ial Black 4A, Spec Ial Black 5, Special Black 6, Nerox 305, Nerox 505, Nerox510, Nerox600, Nerox605 (manufactured by Orion Engineered Carbons); MA7 , MA8, MA100, MA600, MCF-88, No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, No. 2300 (manufactured by Mitsubishi Chemical Corporation) and the like.

Cyan coloring agents include, for example, C.I. I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, 80 and the like.

Examples of magenta coloring agents include C.I. I. Pigment Red 5, 7, 12, 48, 48: 1, 57, 88, 112, 122, 123, 146, 149, 150, 166, 168, 177, 178, 179, 184, 185, 202, 206, 207, 254, 255, 257, 260, 264, 272 and C.I. I. Pigment Violet 19 and the like.

Examples of yellow colorants include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, 180, 185, 213 and the like.

A single coloring agent can be used for any of the above coloring agents. Also, two or more colorants can be used together for the purpose of adjusting the hue.
Also, the water-insoluble colorant is preferably dispersed stably in the dark-colored ink and the light-colored ink. In order to obtain such a dispersion, a surface-treated pigment (also referred to as a self-dispersion pigment) can be used in which dispersibility-imparting groups are chemically imparted to the surface of a water-insoluble colorant. Moreover, a coloring agent obtained by partially or entirely covering the surface of a water-insoluble coloring agent with a polymer dispersant (also referred to as a microcapsule-type coloring agent or the like) can also be used.

[Ink modifier]
The above-mentioned dark-colored ink and light-colored ink include, for example, organic solvents, dispersants, antifoaming agents, antiseptic and antifungal agents, pH adjusters, chelating reagents, rust inhibitors, water-soluble polymer compounds, water-dispersible resins, and the like. of ink modifiers can be included if desired.

The ink preferably contains an organic solvent. A water-soluble organic solvent is preferable as the organic solvent. However, even a sparingly water-soluble organic solvent can be used in combination with a water-soluble organic solvent so long as the ink does not undergo layer separation. In the present specification, the poorly water-soluble organic solvent is generally 3% or less, preferably 2% or less solubility in water at 25°C.
Water-soluble organic solvents include, for example, C1-C6 alkanols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol; N,N-dimethylformamide, N,N-dimethylacetamide, etc. carboxylic acid amides; lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-methylpyrrolidin-2-one; 1,3-dimethylimidazolidin-2-one, 1,3-dimethylhexahydropyrimide Cyclic ureas such as -2-one; ketones or ketoalcohols such as acetone, 2-methyl-2-hydroxypentan-4-one, ethylene carbonate; cyclic ethers such as tetrahydrofuran and dioxane; ethylene glycol, diethylene glycol, propylene glycol , 1,3-propanediol, butylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol (preferably having a molecular weight of 400, 800, 1540, or higher) mono-, oligo- or polyalkylene glycols or thioglycols having C2-C6 alkylene units such as , polypropylene glycol, thiodiglycol, dithiodiglycol; glycerin, diglycerin, hexane-1,2,6-triol, trimethylolpropane C3-C9 polyols (triols) such as; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoallyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether (butyl carbitol) , triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, prolene glycol monobutyl ether, dipropylene glycol monomethyl ether and other glycol ethers (preferably C3-C10 mono, di- or triethylene glycol ethers, and C4-C13 mono-, di- or tripropylene glycol ethers); 1,2-pentanediol, 1,5-pentanediol, 1,2-hexane C5-C9 alkanes such as diols, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, 2,4-diethyl-1,5-pentanediol Diol; γ-butyrolactone, dimethylsulfoxide and the like.

Examples of poorly water-soluble organic solvents include C8-16 (preferably C8-12) alkyls having a hydroxyl group and an acyloxy group, C10-C12 alkanediols, and the like. Specific examples thereof include texanol.

[Dispersant]
When a water-insoluble colorant is contained in the ink, it is preferable to uniformly and stably disperse the colorant in the ink using a dispersant. Examples of dispersing agents include styrene and derivatives thereof; vinylnaphthalene and derivatives thereof; aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids; acrylic acid and derivatives thereof; maleic acid and derivatives thereof; fumaric acid and derivatives thereof; vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and derivatives thereof; hydrophilic monomers), such as block copolymers, random copolymers and graft copolymers. These can be salts or the like, if desired.
The weight average molecular weight of the dispersant is about 1,000 to 30,000, preferably 1,250 to 25,000, more preferably 1,500 to 20,000. The acid value is about 80-300, preferably 90-275, more preferably about 100-250.
Dispersants are also available as commercial products. Specific examples thereof include Joncryl 61J, 67, 68, 450, 55, 555, 586, 678, 680, 682, 683, 690; and B-36; all manufactured by BASF.
Furthermore, as the dispersant, a random copolymer and a block copolymer obtained by copolymerization by a living radical polymerization method can also be used.

Antifoaming agents include, for example, silicone-based, silica-mineral oil-based, olefin-based, and acetylene-based antifoaming agents. Commercially available antifoaming agents include, for example, Surfynol DF37, DF58, DF110D, DF220, MD-20, and Olphine SK-14 all manufactured by Shin-Etsu Chemical Co., Ltd.

Antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, ethyl p-hydroxybenzoate, 1,2-benzisothiazolin-3-one and salts thereof.

Examples of antiseptics include organic sulfur, organic nitrogen sulfur, organic halogen, haloarylsulfone, iodopropargyl, haloalkylthio, nitrile, pyridine, 8-oxyquinoline, benzothiazole, and isothiazoline. dithiol, pyridine oxide, nitropropane, organic tin, phenol, quaternary ammonium salt, triazine, thiazine, anilide, adamantane, dithiocarbamate, brominated indanone, benzylbromoacetate and inorganic salt-based compounds. Specific examples of organic halogen compounds include sodium pentachlorophenol, specific examples of pyridine oxide compounds include sodium 2-pyridinethiol-1-oxide, and isothiazoline compounds include 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4 -isothiazolin-3-one magnesium chloride, 5-chloro-2-methyl-4-isothiazolin-3-one calcium chloride, 2-methyl-4-isothiazolin-3-one calcium chloride and the like. Specific examples of other antiseptic and antifungal agents include anhydrous sodium acetate, sodium sorbate, sodium benzoate, trade names Proxel GXL (S) and Proxel XL-2 (S) manufactured by Arch Chemicals.

Any substance can be used as the pH adjuster as long as it can control the pH of the ink within a predetermined range without adversely affecting the prepared ink. Specific examples thereof include alkanolamines such as diethanolamine, triethanolamine and N-methyldiethanolamine; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide; ammonium hydroxide (ammonia water); Alkali metal carbonates such as lithium carbonate, sodium carbonate, sodium hydrogencarbonate and potassium carbonate; alkali metal salts of organic acids such as sodium silicate and potassium acetate; inorganic bases such as disodium phosphate and the like.

Chelating agents include, for example, disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, sodium uracil diacetate and the like.

Examples of rust preventives include acidic sulfites, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate and dicyclohexylammonium nitrite.

Examples of water-soluble ultraviolet absorbers include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds and triazine compounds.

Examples of water-soluble polymer compounds include polyethylene glycol, polyvinyl alcohol, cellulose derivatives, polyamines and polyimines.

The water-dispersible resin is preferably one that can fix the colorant in the ink to the recording medium by forming a film at room temperature. The resin used for the water-dispersible resin is not particularly limited. mentioned.
A water-based resin emulsion is preferable as the water-dispersible resin.
Specific examples of resin emulsions include Superflex 126, 150, 170, 210, 420, 470, 820, 830, 860, and 890 (urethane resin emulsions manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Hydran HW-350, HW-178, HW-163, HW-171, AP-20, AP-30, AP-40F, WLS-201, WLS-210 (urethane resin emulsion, manufactured by DIC Corporation); 0569, 0850Z, 2108 (styrene -butadiene resin emulsion JSR Corporation); 4001, Boncoat 5454 (acrylic resin emulsion, manufactured by DIC Corporation), and the like.

As the antioxidant, for example, various organic and metal complex anti-fading agents can be used. Examples of the organic anti-fading agents include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, and the like. .

Examples of the method for preparing the ink include stirring and mixing the pigment in an aqueous liquid using a sand mill (bead mill), roll mill, ball mill, paint shaker, ultrasonic disperser, microfluidizer, or the like. An aqueous dispersion is prepared using known methods. An ink can be prepared by adding water and, if necessary, an ink preparation agent and the like to the obtained dispersion liquid and mixing them by a known method using stirring, a homogenizer, or the like. The order of mixing each component of the ink is not particularly limited.

When the ink is used for inkjet recording, it is preferable to remove solid contaminants by microfiltration of the ink. As a method for microfiltration, a known method can be appropriately used. For example, using a filter paper such as glass filter paper GC-50 (retention diameter 0.5 μm, manufactured by Advantech) and glass filter paper GA-100 (retention diameter 1.0 μm, manufactured by Advantech), a method of performing suction filtration, etc. mentioned.

The above ink set can be used in various types of recording. For example, it is suitable for writing instruments, water-based printing, information recording, textile printing, etc., and is particularly preferably used for inkjet recording.

The ink jet recording method is a method of recording by ejecting droplets of each ink of the ink set from an ink jet printer according to a recording signal and depositing them on a recording medium. The ink nozzles and the like used for recording are not particularly limited and can be appropriately selected according to the purpose.

The inkjet printer can use any known recording method. For example, a charge control method that uses electrostatic attraction to eject ink; a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezo element; and an electric signal is converted into an acoustic beam to irradiate the ink, and the ink is emitted. Examples include an acoustic ink jet system in which pressure is used to eject ink; and a thermal ink jet system in which ink is heated to form air bubbles and the resulting pressure is used.
The inkjet recording method also includes a method of improving fixability of a coloring agent by using colorless and transparent ink.
For the purpose of increasing the printing speed, industrial inkjet printers preferably have a configuration of line head type inkjet printers and perform single-pass printing. With the ink described above, even under such printing conditions, a printed image can be obtained in which bleeding between dark and light color inks is suppressed.

The recording medium is not particularly limited, and any material to which the ink set can adhere can be used as the recording medium. Specific examples thereof include recording sheets such as paper and film; fibers and cloth (cellulose, nylon, wool, etc.); leather; base materials for color filters, and the like. Among these, recording sheets are preferred.
Recording sheets can be broadly classified into those having an ink-receiving layer and those not having an ink-receiving layer.
The ink-receiving layer is formed by impregnating or coating a substrate with a cationic polymer; It is provided by a method of machining.
Paper, synthetic paper, film and the like can be used as the substrate.
Information transmission sheets having an ink-receiving layer are usually called inkjet paper, inkjet film, glossy paper, and the like.

Recording sheets having no ink-receiving layer include various papers such as coated papers and art papers used for gravure printing, offset printing, etc.; cast-coated papers used for label printing; OHP sheets; plastic films, etc. is mentioned. The plastic mentioned here includes polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, polypropylene and the like.

When inkjet recording is performed on a recording sheet having no ink-receiving layer, the surface of the recording sheet is preferably modified for the purpose of improving the fixability of the colorant.

As a surface modification method, it is preferable to perform at least one treatment selected from corona discharge treatment, plasma treatment and flame treatment. A known method can be used for these treatments. In addition, it is generally known that the effect of surface modification based on these treatments weakens over time. Therefore, when the surface of the recording sheet is modified, it is preferable to perform ink jet recording immediately.
The surface modification of the recording sheet can be carried out by appropriately adjusting the number of treatments, treatment time, applied voltage, etc. so as to obtain the desired effect. The state of surface modification can be confirmed by measuring the contact angle by a known method or the like.

The inkjet recording method is a method of performing recording using an inkjet printer having a container containing each ink of the ink set.

Unless otherwise specified, all of the components described above can be used singly or in combination of two or more, if desired.
In addition, with respect to all of the above items, a combination of preferable items is more preferable, and a combination of more preferable items is even more preferable. The same applies to a combination of a preferable item and a more preferable item, a combination of a more preferable item and a more preferable item, and the like.

The ink set of the present invention can suppress bleeding between dark-colored inks and light-colored inks. Also, even when printing light-colored images, it is possible to obtain high-quality images without graininess.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples.
Unless otherwise specified, suction filtration was performed using at least one type of filter paper selected from glass filter paper GC-50 and glass filter paper GA-100 when filtration separation was performed.
The content of the colorant in the total mass of the dispersion liquid was calculated as a conversion value of only the content of the colorant by the dry weight method using MS-70 manufactured by A&D Co., Ltd.
The static surface tension of each ink was measured using CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[Preparation Example 1]: Preparation of cyan dispersion A block copolymer described in Synthesis Example 3 of WO 2013/115071 was prepared, and the obtained block copolymer (6 parts) was dissolved in 20 parts of methyl ethyl ketone. to form a homogeneous solution. After adding a mixed solution of sodium hydroxide (0.45 parts) dissolved in water (53.55 parts) to this solution, C.I. I. Pigment Blue 15:4 (manufactured by Dainichiseika Co., Ltd., Chromofine blue 4851, 20 parts) was added and dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. After adding water (100 parts) to the obtained liquid, this liquid was filtered to obtain filtrate. Methyl ethyl ketone and part of water were distilled off from the obtained filtrate under reduced pressure using an evaporator to obtain a cyan dispersion (Cdp) having a pigment content of 11.7%.

[Preparation Example 2]: Preparation of dark cyan inks DC to DC3.
After mixing each component shown in Table 1 below, impurities were filtered off with a 3 μm membrane filter to obtain dark cyan inks DC1 to DC3. The total content of colorants in the total weight of the dark ink was adjusted to 5%.

[Preparation Example 3]: Preparation of light cyan inks LC1 to LC3.
After mixing each component shown in Table 1 below, impurities were filtered off with a 3 μm membrane filter to obtain light-colored cyan inks LC1 to LC3. The total content of colorants in the total weight of the light color ink was adjusted to 1%.

[Preparation Example 4]: Preparation of resin emulsion of water-dispersed resin.
A resin emulsion having an acid value of 6 KOHmg/g and a solid content of 25% was prepared by repeating Preparation Example 4 of WO 2015/147192. This is referred to as Resin 1.

The abbreviations and the like in Table 1 below have the following meanings.
Cdp: Cyan dispersion obtained in Preparation Example 1.
TEG: triethylene glycol.
PG: propylene glycol.
GL-3: Aoki Yushi Co., Ltd., product name Braunon GL-3, polyoxyethylene adduct of glycerin, ethyleneoxy addition mole number 3.
1,2-HD: 1,2-hexanediol.
TEA: triethanolamine.
Tex: Texanol.
BYK-349: manufactured by BYK-Chemie, trade name BYK-349.
FS-31: manufactured by Chemours, trade name Capstone FS-31.
SF465: An acetylene glycol-based surfactant manufactured by Nissin Kagaku Kogyo Co., Ltd., trade name Surfynol 465.
Resin 1: Emulsion water of water-dispersible resin obtained in Preparation Example 4: Ion-exchanged water.

[Bleeding evaluation test (1)]
Ink sets of Examples 1 to 4 and Comparative Examples 1 to 5 were prepared by combining dark color inks and light color inks shown in Tables 2 and 3 below.
Using an inkjet printer equipped with an inkjet head KJ4B-QA (manufactured by Kyocera Corporation), dark-colored ink and light-colored ink of the above ink set are crossed in a cross shape on Raicho coated paper (manufactured by Chuetsu Pulp Industry Co., Ltd.). Inkjet recording was performed in the same manner as above to obtain a test piece.
After drying the obtained test piece at room temperature for about 24 hours, "bleeding" at the intersection of the dark-colored ink and the light-colored ink was visually observed, and evaluated according to the following three grades of evaluation criteria from A to C. . The evaluation results are shown in Tables 2 and 3 below.
The values in parentheses in the table below are the measured values of the static surface tension of each ink. Its unit is "mN/m".
In Tables 2 and 3 below, "StD-StL" is a numerical value obtained by subtracting the static surface tension "StL" of light-colored ink from the static surface tension "StD" of dark-colored ink.
[Evaluation criteria]
A: Bleeding is hardly recognized, and there is no practical problem at all.
B: Bleeding is slightly observed, but does not pose a practical problem.
C: Obvious blurring is observed, and the quality is not practical.

As can be seen from Tables 2 and 3 above, ink sets in which the surface tensions of both the dark ink and the light color ink are 27 mN/m or less, and the difference in surface tension between the dark ink and the light color ink is within ±4, bleeding is observed. It can be seen that bleeding clearly occurs with other ink sets.
No bleeding was observed in any of the test pieces obtained with the ink sets of Examples 1 to 4, showing good results.

[Preparation Example 5]: Preparation of Yellow Dispersion The C.I. I. Pigment Blue 15:4 instead of C.I. I. A yellow dispersion (Ydp) having a pigment content of 11.9% was obtained in the same manner as in Preparation Example 1 except that Pigment Yellow 74 (HANSA Yellow 5GX01 manufactured by Clariant) was used.

[Preparation Example 6]: Preparation of dark yellow inks DY1 and DY2 After mixing each component shown in Table 4 below, impurities were filtered out with a 3 μm membrane filter to obtain dark yellow ink DY1. and DY2 were obtained. The total content of colorants in the total weight of the dark ink was adjusted to 5%.

[Preparation Example 7]: Preparation of light-colored yellow ink LY1 After mixing each component shown in Table 4 below, contaminants were filtered off with a 3 μm membrane filter to obtain light-colored yellow ink LY1. The total content of colorants in the total weight of the light color ink was adjusted to 1%.

[Preparation Example 8]: Preparation of Magenta Dispersion The C.I. I. Pigment Blue 15:4 instead of C.I. I. A magenta dispersion (Mdp) having a pigment content of 12.2% was obtained in the same manner as in Preparation Example 1 except that Pigment Magenta 122 (Inkjet Magenta E02VP2621 manufactured by Clariant) was used.

[Preparation Example 9]: Preparation of dark magenta inks DM1 and DM2 After mixing each component shown in Table 4 below, impurities were filtered out with a 3 μm membrane filter to obtain dark magenta ink DM1. and DM2. The total content of colorants in the total weight of the dark ink was adjusted to 5%.

[Preparation Example 10]: Preparation of light-colored magenta ink LM1 After mixing each component shown in Table 4 below, impurities were filtered out with a 3 μm membrane filter to obtain light-colored magenta ink LM1. The total content of colorants in the total weight of the light color ink was adjusted to 1%.

[Preparation Example 11]: Preparation of dark cyan ink DC4.
After mixing each component shown in Table 4 below, impurities were filtered out with a 3 μm membrane filter to obtain a dark cyan ink DC4. The total content of colorants in the total weight of the dark ink was adjusted to 5%.

New abbreviations and the like used in Table 4 below have the following meanings. Other than these, the abbreviations and the like in Table 1 above have the same meanings.
Ydp: Yellow dispersion obtained in Preparation Example 5.
Mdp: Magenta dispersion obtained in Preparation Example 8.

[Bleeding evaluation test (2)]
Ink sets of Examples 5 to 7 and Comparative Examples 6 to 8 were prepared by combining dark color inks and light color inks shown in Tables 5 and 6 below.
Except for using the obtained ink set, visually observe "bleeding" at the intersection of the dark color ink and the light color ink in the same manner as in "[Bleeding evaluation test (1)]" above. It was evaluated according to C's three-grade evaluation criteria. The evaluation results are shown in Tables 5 and 6 below.
The values in parentheses in the table below are the measured values of the static surface tension of each ink. Its unit is "mN/m".
In Tables 5 and 6 below, "StD-StL" is a numerical value obtained by subtracting the static surface tension "StL" of light-colored ink from the static surface tension "StD" of dark-colored ink.

As can be seen from Tables 5 and 6 above, the surface tension of both the dark ink and the light color ink is 27 mN/m or less, and the difference in surface tension between the dark ink and the light color ink is within ±4. As in the case of the ink set shown in No. 2, no bleeding was observed, whereas the other ink sets clearly caused bleeding.
No bleeding was observed in any of the test pieces obtained with the ink sets of Examples 5 to 7, showing good results.

The ink set of the present invention is extremely useful as an ink set for ink jet recording because bleeding between dark and light colors is suppressed.

Claims (9)

A water-based inkjet recording ink set comprising a water-based dark ink and a water-based light color ink having different colorant contents in the total mass of the ink, wherein the dark color ink and the light color ink contain a colorant Both contain a water-insoluble colorant, the water-insoluble colorant is a pigment, the content of the colorant in the dark ink is 3 to 7%, and the static surface of the dark ink and the light color ink An ink set in which each tension is 27 mN/m or less, and the value obtained by subtracting the static surface tension of the light-colored ink from the static surface tension of the dark-colored ink is within ±4 mN/m. However, the dark-colored ink and the light-colored ink mentioned above exclude active energy ray-curable ink that is cured by irradiation with an active energy ray. 2. The ink set according to claim 1, wherein at least one of the dark-colored ink and the light-colored ink contains a surfactant selected from silicone-based surfactants and fluorine-based surfactants. 3. The ink set according to claim 2 , wherein both the dark-colored ink and the light-colored ink contain surfactants selected from silicone surfactants and fluorosurfactants. 4. The ink set according to any one of claims 1 to 3 , further comprising an organic solvent. 5. An inkjet recording method, wherein droplets of each ink of the ink set according to any one of claims 1 to 4 are ejected from an inkjet printer according to a recording signal, and deposited on a recording medium for recording. 6. The ink jet recording method according to claim 5 , wherein the recording medium is an ink-absorbing recording medium or an ink-non-absorbing recording medium. A recording medium to which each ink of the ink set according to any one of claims 1 to 4 is adhered. An inkjet printer comprising a container containing each ink of the ink set according to any one of claims 1 to 4 . A method for suppressing inter-color bleeding of dark-colored ink and light-colored ink, using the ink set according to any one of claims 1 to 4 .