JP7225861B2 - Ink set, printing device, and printing method - Google Patents

Description

The present invention relates to an ink set, a printing apparatus, and a printing method.

Compared to other recording methods, the inkjet recording method has a simpler process and can easily produce full-color images. , is expanding into the field of industrial printing.

High productivity is required in the field of industrial printing. 2. Description of the Related Art In the field of sign graphics such as advertisements displayed indoors and outdoors, wide-width inkjet printers are on the market, but there is a high demand for improved productivity. In a wide-width inkjet printing apparatus, a multi-pass method is generally used in which the head scans in the media width direction (main scanning direction) and the media is conveyed perpendicularly (sub-scanning direction) to the head scanning direction. In order to improve the productivity in such a multi-pass method, in order to increase the printing area in one pass, a plurality of nozzle rows in which a plurality of nozzle holes for ejecting ink are arranged in the sub-scanning direction perpendicular to the main scanning direction. Although it is effective to use a head equipped with such a head, it has the side effect of making it easier for ink droplets to land in a different position.

For this reason, for example, using an ink set of yellow ink, magenta ink, and cyan ink, the problem is to prevent the occurrence of gloss unevenness due to ink droplet impact deviation during reciprocation of the head. It has been proposed to adjust the type of ink ejected from the nozzle (see, for example, Patent Document 1).
In addition, the pigment content in the cyan ink, magenta ink, and yellow ink is 1.5 to 6% by weight, respectively, and the pigment content ratio is cyan:magenta:yellow=1:1 to 2:1 to 3. A water-based inkjet ink set has been proposed (see, for example, Patent Document 2).

An object of the present invention is to provide an ink set that can suppress the occurrence of color unevenness.

The ink set of the present invention as a means for solving the above-mentioned problems is an ink set containing a black pigment-containing ink, a cyan pigment-containing ink, a magenta pigment-containing ink, and a yellow pigment-containing ink. and satisfy the following equations (1) and (2).
Black pigment content>Yellow pigment content>Cyan pigment content Formula (1)
Magenta pigment content>Yellow pigment content>Cyan pigment content Formula (2)

According to the present invention, it is possible to provide an ink set that can suppress the occurrence of color unevenness.

FIG. 1 is a schematic diagram showing an example of the configuration of a printing apparatus. FIG. 2 is a plan view showing an example of the nozzle configuration of the recording head.

(ink set)
The ink set of the present invention includes an ink containing a black pigment, an ink containing a cyan pigment, an ink containing a magenta pigment, and an ink containing a yellow pigment, wherein the ink set is represented by the following formulas (1) and ( 2) and, if necessary, contain other ingredients.
Black pigment content>Yellow pigment content>Cyan pigment content Formula (1)
Magenta pigment content>Yellow pigment content>Cyan pigment content Formula (2)

The conventional technique disclosed in Japanese Patent Application Laid-Open No. 2002-200300 has a problem that it is impossible to prevent ink drop landing deviation from occurring when it is used in a wide-width printing apparatus having a head in which a plurality of nozzle rows are arranged.
The prior art described in Patent Document 2 has excellent printability on general printing substrates, especially substrates with low water absorption such as coated paper, art paper and vinyl chloride sheets, and printed matter with high weather resistance and color gamut. The problem is not to suppress the occurrence of color unevenness. Further, in Patent Document 2, since the content of cyan pigment in the cyan ink in the ink set is as high as 1.5% by mass or more, there is a problem that the occurrence of color unevenness on non-permeable recording media cannot be suppressed. be.

An ink set containing a black pigment-containing ink, a cyan pigment-containing ink, a magenta pigment-containing ink, and a yellow pigment-containing ink satisfies the above formulas (1) and (2), preferably Printing with ejection means having four or more nozzle rows in which a plurality of nozzle holes for ejecting ink are arranged in the sub-scanning direction orthogonal to the main scanning direction by satisfying the following formula: black pigment content = magenta pigment content The present inventors have found that when used in an apparatus, it is possible to provide an ink set capable of achieving high productivity and suppressing the occurrence of color unevenness.

Since color unevenness is particularly easy to recognize in cyan, the effect of suppressing color unevenness is high by lowering the density of one dot of ink containing a cyan pigment.
In the present invention, it is preferable to satisfy the following formula, black pigment content=magenta pigment content, from the viewpoint of suppressing the occurrence of color unevenness, and the black pigment content and the magenta pigment content are 2% by mass or more and 4% by mass % or less, and the absolute value of the difference (CB) between the magenta pigment content C and the cyan pigment content B is 0.8% by mass or more and 3% by mass or less. It is more preferable from the point of further suppression.
Each ink in the ink set preferably contains water, an organic solvent, and a resin, and more preferably contains a surfactant.
Inks used for inkjet include water-based inks containing water and organic solvents, and solvent inks containing mainly organic solvents as liquid components.
In order to obtain the effects of the present invention, it is preferable that the ink be a water-based ink and further contain a urethane resin.
Not only is it difficult for pigments to adhere to non-permeable recording media such as polyvinyl chloride (PVC) and polyethylene terephthalate (PET), fine irregularities occur on the image surface when the amount of adhesion between colors differs. This causes color unevenness. By including the urethane resin in the ink, it is possible to achieve both improvement in fixability to a non-permeable recording medium and improvement in uniformity of the image surface.

The ink set of the present invention is preferably used in a wide-width printing apparatus having ejection means having four or more nozzle rows in which a plurality of nozzle holes for ejecting ink are arranged in a sub-scanning direction perpendicular to the main scanning direction. It is more preferable to use in a wide printing apparatus having eight or more ejection means. This enables high-speed printing and significantly improves productivity.

As a method for analyzing each ink in the ink set and measuring the content of the pigment contained in each ink, each ink is separated into a supernatant liquid and a sediment by centrifugation, then the sediment is collected, The pigment is collected by repeating washing with an organic solvent and filtration. The content can be obtained by weighing the collected pigment. Further, the structure of the pigment can be confirmed by performing data analysis through GC-MS analysis.
[Centrifugation]
・ Apparatus: himac CS150GX manufactured by Hitachi Koki Co., Ltd.
・Rotation speed: 150,000 rpm
・Rotation time: 1 hour
[GC-MS]
・Apparatus: QP5000 manufactured by Shimadzu Corporation
・Column: Ultra ALLOY-5L=30m, ID=0.25mm Film=0.25μm
・Column temperature rise: 50°C to 330°C
・Column flow rate: 1.0 mL/min
・Split: 1:100
・Ionization method: EI method (70 eV)
・Measuring mass range: m/z 33 to 600
・Data analysis, analysis software: GCMSsolution manufactured by Shimadzu Corporation

The ink containing a black pigment, the ink containing a cyan pigment, the ink containing a magenta pigment, and the ink containing a yellow pigment, which constitute the ink set of the present invention, will be described. Hereinafter, these are sometimes collectively referred to simply as "ink".
For example, inks containing cyan pigments include cyan inks and light cyan inks, and inks containing cyan pigments with different concentrations of cyan pigments.

<Ink>
Organic solvents, water, coloring materials, resins, additives, and the like used in the ink are described below.

<Organic solvent>
The organic solvent used in the present invention is not particularly limited, and any water-soluble organic solvent can be used. Examples thereof include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.
Examples of water-soluble organic solvents include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2 , 3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2, 4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1 , 2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3 - Polyhydric alcohols such as pentanediol and petriol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, etc. Polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1, Nitrogen-containing heterocyclic compounds such as 3-dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone, formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide , 3-butoxy-N, N-dimethylpropionamide and other amides, monoethanolamine, diethanolamine, triethylamine and other amines, dimethylsulfoxide, sulfolane, thiodiethanol and other sulfur-containing compounds, propylene carbonate, ethylene carbonate, and the like. be done. These may be used individually by 1 type, and may use 2 or more types together.
It is preferable to use an organic solvent having a boiling point of 250° C. or less because it not only functions as a wetting agent but also provides good drying properties.

Polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used.
Examples of polyol compounds having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.
Examples of glycol ether compounds include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether. such as polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

<Water>
The content of water in the ink is not particularly limited and can be appropriately selected according to the purpose. % or more and 60 mass % or less is more preferable.

<Pigment>
An inorganic pigment or an organic pigment can be used as the pigment. These may be used individually by 1 type, and may use 2 or more types together. Mixed crystals may also be used.
Examples of pigments that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, glossy color pigments such as gold and silver, and metallic pigments.
Inorganic pigments include, for example, titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow, as well as known methods such as the contact method, furnace method, and thermal method. carbon black can be used.
Examples of organic pigments include azo pigments and polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.). , dye chelates (eg, basic dye chelates, acid dye chelates, etc.), nitro pigments, nitroso pigments, aniline black, and the like. Among these pigments, those having good affinity with the solvent are preferably used. In addition, resin hollow particles and inorganic hollow particles can also be used.
Specific examples of pigments for black include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black and channel black, or copper and iron (C.I. Pigment Black 11). , metals such as titanium oxide, and organic pigments such as aniline black (C.I. Pigment Black 1).
Further, for color, C.I. I. Pigment yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104 , 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, C.I. I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53: 1, 57:1 (brilliant carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (red red), 104, 105, 106, 108 (cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C.I. I. Pigment Violet 1 (rhodamine lake), 3, 5:1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15 (phthalocyanine blue), 15:1, 15:2, 15:3, 15:4 (phthalocyanine blue), 16, 17:1, 56, 60, 63, C.I. I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36 and the like. These may be used individually by 1 type, and may use 2 or more types together.

In order to disperse the pigment and obtain an ink, there are a method of introducing a hydrophilic functional group into the pigment to make it a self-dispersing pigment, a method of coating the surface of the pigment with a resin for dispersion, and a method of dispersing using a dispersant. methods and the like.
As a method of making a self-dispersing pigment by introducing a hydrophilic functional group into a pigment, for example, a method of adding a functional group such as a sulfone group or a carboxyl group to a pigment (for example, carbon) to make it dispersible in water. is mentioned.
As a method of coating the surface of a pigment with a resin and dispersing it, there is a method of encapsulating the pigment in microcapsules to make it dispersible in water. This can be rephrased as a resin-coated pigment. In this case, all the pigments mixed in the ink need not be coated with a resin, and uncoated pigments or partially coated pigments may be dispersed in the ink as long as the effects of the present invention are not impaired. may be
Examples of the method of dispersing using a dispersant include a method of dispersing using a known low-molecular-weight dispersant and high-molecular-weight dispersant typified by surfactants.
As the dispersant, it is possible to use, for example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. depending on the pigment.
RT-100 (nonionic surfactant) manufactured by Takemoto Oil & Fat Co., Ltd. and sodium naphthalenesulfonate formalin condensate can also be suitably used as a dispersant.
A dispersant may be used individually by 1 type, and may use 2 or more types together.

<Pigment dispersion>
Inks can be obtained by mixing materials such as water and organic solvents with pigments. Ink can also be produced by mixing a pigment, water, a dispersant, and the like to form a pigment dispersion, and then mixing materials such as water and an organic solvent.
The pigment dispersion is obtained by mixing and dispersing water, a pigment, a pigment dispersant, and optionally other components, and adjusting the particle size. Dispersion should be carried out using a disperser.
The particle diameter of the pigment in the pigment dispersion is not particularly limited, but the dispersion stability of the pigment is improved, and the image quality such as ejection stability and image density is improved. 500 nm or less is preferable, and 20 nm or more and 150 nm or less is more preferable. The particle size of the pigment can be measured using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell Co., Ltd.).
The content of the pigment in the pigment dispersion is not particularly limited and can be appropriately selected according to the purpose. % or more and 50 mass % or less is preferable, and 0.1 mass % or more and 30 mass % or less is more preferable.
The pigment dispersion is preferably degassed by filtering coarse particles with a filter, a centrifugal separator, or the like, if necessary.

<Resin>
The type of resin contained in the ink is not particularly limited and can be appropriately selected according to the purpose. resins, styrene-butadiene-based resins, vinyl chloride-based resins, acrylic-styrene-based resins, acrylic-silicone-based resins, and the like. Among these, urethane resins are particularly preferable from the viewpoint of adhesion to impermeable recording media.
Resin particles made of these resins may also be used. Ink can be obtained by mixing resin particles in a resin emulsion state in which water is dispersed as a dispersion medium with a material such as a coloring material or an organic solvent. As the resin particles, appropriately synthesized ones may be used, or commercially available products may be used. These may be used individually by 1 type, and may use 2 or more types together.
The volume average particle diameter of the resin particles is not particularly limited and can be appropriately selected according to the intended purpose. It is more preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 100 nm or less.
The volume average particle diameter can be measured, for example, using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell Co., Ltd.).
The content of the resin is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoint of fixability and storage stability of the ink, the content is 1% by mass or more and 30% by mass based on the total amount of the ink. The following is preferable, 3 to 10 mass % is more preferable, and 3 to 5 mass % is even more preferable.

The particle size of the solid content in the ink is not particularly limited and can be appropriately selected according to the purpose. is preferably 20 nm or more and 1,000 nm or less, more preferably 20 nm or more and 150 nm or less. The solid content includes resin particles, pigment particles, and the like. The particle size can be measured using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrack Bell Co., Ltd.).

<Additive>
Surfactants, antifoaming agents, antiseptic and antifungal agents, antirust agents, pH adjusters, etc. may be added to the ink, if necessary.

-Surfactant-
Any of silicone surfactants, fluorosurfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used as surfactants.
The silicone-based surfactant is not particularly limited and can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferable. Those having an oxyethylene group or a polyoxyethylene polyoxypropylene group are particularly preferred because they exhibit good properties as water-based surfactants. As the silicone-based surfactant, a polyether-modified silicone-based surfactant can also be used, and examples thereof include compounds in which a polyalkylene oxide structure is introduced into the side chain of the Si portion of dimethylsiloxane.

Examples of fluorine-based surfactants include perfluoroalkylsulfonic acid compounds, perfluoroalkylcarboxylic acid compounds, perfluoroalkylphosphoric acid ester compounds, perfluoroalkylethylene oxide adducts, and perfluoroalkyl ether groups in side chains. Polyoxyalkylene ether polymer compounds are particularly preferred due to their low foaming properties. Examples of the perfluoroalkylsulfonic acid compound include perfluoroalkylsulfonic acid and perfluoroalkylsulfonate. Examples of the perfluoroalkylcarboxylic acid compounds include perfluoroalkylcarboxylic acids and perfluoroalkylcarboxylic acid salts. As the polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in a side chain, a sulfate ester salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in a side chain, and a perfluoroalkyl ether group in a side chain Examples thereof include salts of polyoxyalkylene ether polymers. Counter ions _of salts _in these fluorosurfactants include Li, Na, _K , _NH4 , _NH3CH2CH2OH , _NH2 ( _CH2CH2OH ) _{2 ,} and NH( _CH2CH2OH ). ₃ and the like.

Amphoteric surfactants include, for example, laurylaminopropionate, lauryldimethylbetaine, stearyldimethylbetaine, lauryldihydroxyethylbetaine and the like.
Nonionic surfactants include, for example, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan Examples include fatty acid esters and ethylene oxide adducts of acetylene alcohol.
Examples of anionic surfactants include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, laurate, polyoxyethylene alkyl ether sulfate and the like.
These may be used individually by 1 type, and may use 2 or more types together.
The content of the surfactant in the ink is not particularly limited and can be appropriately selected according to the purpose. % or more and 5 mass % or less is preferable, and 0.05 mass % or more and 5 mass % or less is more preferable.

- Defoamer -
The antifoaming agent is not particularly limited, and examples thereof include silicone antifoaming agents, polyether antifoaming agents, and fatty acid ester antifoaming agents. These may be used individually by 1 type, or may use 2 or more types together. Among these, silicone-based antifoaming agents are preferred because of their excellent foam breaking effect.

- Antiseptic and antifungal agent -
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

-anti-rust-
The rust inhibitor is not particularly limited, and examples thereof include acidic sulfites and sodium thiosulfate.

-pH adjuster-
The pH adjuster is not particularly limited as long as it can adjust the pH to 7 or higher, and examples thereof include amines such as diethanolamine and triethanolamine.

The physical properties of the ink are not particularly limited and can be appropriately selected depending on the intended purpose. For example, viscosity, surface tension, pH and the like are preferably within the following ranges.
The viscosity of the ink at 25° C. is preferably 5 mPa·s or more and 30 mPa·s or less, more preferably 5 mPa·s or more and 25 mPa·s or less, from the viewpoint of improving the print density and character quality and obtaining good ejection properties. more preferred. Here, for viscosity, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used. Measurement conditions are 25° C., standard cone rotor (1°34′×R24), sample liquid volume 1.2 mL, rotation speed 50 rpm, 3 minutes.
The surface tension of the ink is preferably 35 mN/m or less, more preferably 32 mN/m or less at 25° C., from the viewpoint that the ink is appropriately leveled on the recording medium and the drying time of the ink is shortened.
The pH of the ink is preferably from 7 to 12, more preferably from 8 to 11, from the viewpoint of preventing corrosion of metal members in contact with the liquid.

<Recording medium>
The recording medium is not particularly limited, and plain paper, glossy paper, special paper, cloth, and the like can be used.
The non-permeable substrate is a substrate having a surface with low water permeability and low absorbency, and includes materials that do not open to the outside even if there are many cavities inside. , refers to a substrate having a water absorption of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method.
As the impermeable substrate, for example, plastic films such as vinyl chloride resin films, polyethylene terephthalate (PET) films, polypropylene, polyethylene and polycarbonate films can be suitably used.

The recording medium is not limited to those used as general recording media, and wallpaper, floor materials, building materials such as tiles, cloth for clothing such as T-shirts, textiles, leather, and the like can be used as appropriate. Ceramics, glass, metal, etc. can also be used by adjusting the configuration of the path for conveying the recording medium.

<Records>
The ink recorded matter of the present invention has an image formed on a recording medium using the ink set of the present invention.
A recorded matter can be obtained by recording with an inkjet recording apparatus and an inkjet recording method.

<Recording device>
FIG. 1 is a schematic diagram showing the configuration of an inkjet recording apparatus 1. As shown in FIG. An inkjet recording apparatus 1, which is a printing apparatus, is a serial type inkjet recording apparatus. As shown in FIG. 1 , the inkjet recording apparatus 1 includes an image forming section 2 that prints a desired image, a drying device 3 , a roll media storage section 4 and a transport mechanism 5 . The roll media storage unit 4 stores roll media (recording media) 40 . Note that the roll media storage unit 4 can store recording media 40 having different sizes in the width direction. The recording medium 40 may be a non-permeable medium such as PVC (vinyl chloride) or PET (polyethylene terephthalate) film, or a permeable medium such as cloth or synthetic paper.

The transport mechanism 5 constitutes a roll-to-roll transport means. The transport mechanism 5 includes a pair of nip rollers 51 , a pair of driven rollers 52 and a take-up roller 53 on a transport path 54 for the recording medium 40 . The nip roller 51 is provided on the front side of the image forming section 2 (on the upstream side in the transport direction A). The nip rollers 51 convey the nipped recording medium 40 toward the image forming section 2 by rotating as the motor is driven. The take-up roller 53 rotates as the motor M is driven to take up the recording medium 40 after printing. The driven roller 52 rotates following the conveyance of the recording medium 40 .

The transport mechanism 5 has a wheel encoder for detecting the transport speed. The conveying mechanism 5 is controlled in conveying speed by controlling a motor based on a target value and a speed detection value obtained by sampling detection pulses from the wheel encoder 55 .

That is, the recording medium 40 stored in the roll media storage section 4 is conveyed to the image forming section 2 through the driven roller 52 by the rotation of the nip roller 51 . A desired image is printed by the image forming section 2 on the recording medium 40 that has reached the image forming section 2 . The recording medium 40 after printing is wound up by the rotation of the winding roller 53 .

The image forming section 2 has a carriage 21 . The carriage 21 is slidably held by guide rods (guide rails) 22 . As the motor M is driven, the carriage 21 moves on a guide rod (guide rail) 22 in a direction (main scanning direction) perpendicular to the transport direction A of the recording medium 40 . More specifically, the carriage 21 moves within a recording area in which the image forming section 2 can print on the recording medium 40 conveyed by the conveying mechanism 5 in the main scanning area which is a movable area in the main scanning direction. move back and forth.

A carriage 21 carries a recording head 20 having a plurality of nozzle holes, which are ejection openings for ejecting droplets. Note that the recording head 20 is integrally provided with a tank that supplies ink to the recording head 20 . However, the recording head 20 is not limited to the one integrally provided with the tank, and may be provided with the tank separately. The recording head 20 functions as a liquid ejection unit, and ejects ink droplets of black (K), yellow (Y), magenta (M), and cyan (C), which are process color recording liquids. . Black (K), yellow (Y), magenta (M), and cyan (C) are inks for image formation.

The image forming section 2 includes a platen 23 that supports the recording medium 40 below the recording head 20 during printing by the recording head 20 .

The image forming section 2 also includes an encoder sheet for detecting the main scanning position of the carriage 21 along the main scanning direction of the carriage 21 . The carriage 21 also has an encoder. The image forming section 2 detects the main scanning position of the carriage 21 by reading the encoder sheet with the encoder of the carriage 21 .

The carriage 21 has a sensor 24 that optically detects the edge of the recording medium 40 as the carriage 21 moves. A detection signal from the sensor 24 is used to calculate the position of the edge of the recording medium 40 in the main scanning direction and the width of the recording medium 40 .

The drying device 3 includes a preheater 30 , a platen heater 31 , a drying heater 32 and a hot air fan 33 . The preheater 30, the platen heater 31, and the drying heater 32 are electric heaters using, for example, ceramic or nichrome wire.

The preheater 30 is provided upstream in the transport direction A of the recording medium 40 with respect to the image forming section 2 . The preheater 30 preliminarily heats the recording medium 40 transported by the transport mechanism 5 .

The platen heater 31 is arranged on the platen 23 . The platen heater 31 heats the recording medium 40 on which the ink droplets ejected from the nozzle holes of the recording head 20 land.

The drying heater 32 is provided downstream of the image forming section 2 in the conveying direction A of the recording medium 40 . The drying heater 32 continues to heat the recording medium 40 printed by the image forming section 2 to promote drying of the ink droplets that have landed.

The hot air fan 33 is provided downstream in the conveying direction A of the recording medium 40 with respect to the drying heater 32 (image forming section 2). The hot air fan 33 blows hot air onto the recording surface of the recording medium 40 on which the ink has landed. The hot air fan 33 blows hot air directly onto the ink on the recording surface of the recording medium 40 to reduce the humidity of the atmosphere around the recording surface of the recording medium 40 and dry it completely.

By installing such a drying device 3, the inkjet recording apparatus 1 employs a non-permeable medium such as a polyvinyl chloride film, a polyethylene terephthalate (PET) film, an acrylic film, or the like, into which ink does not permeate, as the recording medium 40. can do.

Note that in the inkjet recording apparatus 1 that forms an image by ejecting ink from the recording head 20 while the carriage 21 reciprocates across the width of the recording medium 40, ink is ejected to form an image only when the carriage is moving forward. There are unidirectional printing that forms an image and bidirectional printing that forms an image by ejecting ink in both forward and backward carriage operations. The inkjet recording apparatus 1 mainly uses bidirectional printing, which is advantageous in terms of printing speed. Here, the operation of ejecting ink from the recording head 20 while the carriage 21 moves in the main scanning direction is assumed to be one scan.

For the control configuration of the inkjet recording apparatus 1, for example, reference can be made to the description in Japanese Patent Application Laid-Open No. 2017-105193.

Next, a liquid ejection head (hereinafter also referred to as a "recording head") of the inkjet recording apparatus 1 will be described.
In the ink set of the present invention, nozzle holes for ejecting at least one of ink containing a cyan pigment, ink containing a magenta pigment, and ink containing a yellow pigment are arranged in the sub-scanning direction orthogonal to the main scanning direction. It can be suitably used for a liquid ejection head having three or more nozzle rows.
Here, FIG. 2 is a plan view showing the nozzle configuration of the recording head 20. As shown in FIG. FIG. 2 transparently shows the nozzle rows of the recording head 20 from above. As shown in FIG. 2, the recording head 20 includes a first nozzle group 20a, a second nozzle group 20b, and a third nozzle group 20c.

FIG. 2 shows an example in which the nozzle groups 20a, 20b, and 20c are arranged in two rows in the main scanning direction and alternately arranged in a zigzag pattern in the sub-scanning direction. That is, the nozzle groups 20a, 20b, and 20c are configured so that the nozzle rows do not overlap from the upstream side to the downstream side in the conveying direction A of the recording medium 40 so that the third nozzle group 20c, the second nozzle group 20b, the third They are arranged in order of one nozzle group 20a. Also, as shown in FIG. 2, the second nozzle group 20b is an example in which the positions of the first nozzle group 20a and the third nozzle group 20c are shifted in the main scanning direction.

The first nozzle group 20a, the second nozzle group 20b, and the third nozzle group 20c use black (K), yellow (Y), magenta (M), and cyan (C), which are process color recording liquids for image formation. It has four rows of nozzles for ejecting ink droplets. Each nozzle row has a nozzle number No. No. 1 nozzle hole to No. 1 nozzle hole. It has 192 nozzle holes of 192 nozzle holes. In the example shown in FIG. 2, each nozzle hole has a nozzle number No. 1 from the nozzle hole on the downstream side in the conveying direction A of the recording medium 40 toward the nozzle hole on the upstream side. 1 to nozzle number No. 192. In this example, the pitch P between these nozzle holes is 150 dpi (dots per inch).

As shown in FIG. 2, the first nozzle group 20a, the second nozzle group 20b, and the third nozzle group 20c each include an ink nozzle array NC containing a cyan pigment that ejects cyan (C) ink droplets, and an ink nozzle array NC that ejects magenta ink droplets. An ink nozzle array NM containing a magenta pigment that ejects ink droplets of (M), an ink nozzle array NY that contains a yellow pigment that ejects ink droplets of yellow (Y), and an ink droplet of black (K). and an ink nozzle array NK containing a black pigment.

In the second nozzle group 20b as well, each row has a nozzle number No. 1 in the same manner as in the first nozzle group 20a. 1 to nozzle number No. It has four rows of nozzles each having 192 nozzle holes. In the second nozzle group 20b as well as in the first nozzle group 20a, the pitch P between the nozzle holes is 150d.
This is an example of pi.

As described above, the nozzle groups 20a, 20b, and 20c have the same number of nozzle rows and the same number of nozzles. Since it can be reduced, the cost of the device can be reduced.

In this embodiment, the nozzle rows of the nozzle groups 20a, 20b, and 20c are arranged along the conveying direction A of the recording medium 40, but the nozzle rows are arranged obliquely to the conveying direction A. may be set.
In FIG. 2, the first nozzle group 20a, the second nozzle group 20b, and the third nozzle group 20c respectively include ink nozzle arrays NC containing cyan pigments for ejecting cyan (C) ink droplets, and magenta (M) ink droplets. an ink nozzle row NM containing a magenta pigment that ejects ink droplets of , an ink nozzle row NY that contains a yellow pigment that ejects yellow (Y) ink droplets, and a black pigment that ejects black (K) ink droplets. However, the configuration is not limited to this, and among the first nozzle group 20a, the second nozzle group 20b, and the third nozzle group 20c, all the nozzles of the first nozzle group 20a may contain a magenta pigment, all nozzles in the second nozzle group 20b may contain a yellow pigment, and all nozzles in the third nozzle group 20c may contain a cyan pigment.
By using the ink set of the present invention, the problem of the present invention, color unevenness, can be resolved.
The ink used in the ink set of the present invention has a low pigment content, but by increasing the number of ejected droplets, the amount of adhered pigment is increased, which leads to elimination of color unevenness.
Also, two sets of nozzle groups as shown in FIG. 2 may be combined to provide six or more nozzle rows. By setting the number of nozzle rows to 6 or more, the speed can be further increased.

In the present invention, the terms image formation, recording, printing, and printing are all synonymous.
The terms recording medium, medium, and printed material are all synonymous.

Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Production Example 1 of Pigment Dispersion)
<Preparation of Cyan Pigment Dispersion>
A cyan pigment dispersion was obtained in the same manner as described in JP-A-2012-207202, "[Pigment Surface Modification Treatment]-Method A-".
Specifically, C.I. I. Pigment Blue 15:3 (trade name: Chromofine Blue, manufactured by Dainichiseika Kogyo Co., Ltd.) 20 g, 20 mmol of the compound of the following structural formula (1), and 200 mL of ion-exchanged water were mixed in a Silverson mixer at room temperature (25° C.). (6,000 rpm (0.6% by mass)) to obtain a slurry. If the pH of the resulting slurry was higher than 4, 20 mmol of nitric acid was added. After 30 minutes, sodium nitrite (20 mmol) dissolved in a small amount of deionized water was slowly added to the above slurry. Further, the mixture was heated to 60° C. with stirring and reacted for 1 hour. The above C.I. I. A modified pigment was obtained by adding a compound of the following structural formula (1) to the surface of Pigment Blue 15:3.
The modified pigment dispersion was then obtained after 30 minutes by adjusting the pH to 10 with an aqueous NaOH solution. Ultrafiltration using a dialysis membrane is performed using the modified pigment dispersion and ion-exchanged water, and then ultrasonic dispersion is performed to obtain a pigment concentration of 15% by mass. A cyan pigment dispersion (self-dispersion type) was obtained.

[Structural formula (1)]

(Production Example 2 of Pigment Dispersion)
<Preparation of Magenta Pigment Dispersion>
In Production Example 1 of Pigment Dispersion, C.I. I. Pigment Blue 15:3 (trade name: Chromofine Blue, manufactured by Dainichiseika Kogyo Co., Ltd.) was added to 20 g of C.I. I. Pigment Red 122 (trade name: Toner Magenta EO02, manufactured by Clariant Japan Co., Ltd.) was changed to 20 g in the same manner as in Pigment Dispersion Production Example 1 to prepare a magenta pigment dispersion having a pigment concentration of 15% by mass. bottom.

(Production Example 3 of Pigment Dispersion)
<Preparation of Yellow Pigment Dispersion>
In Production Example 1 of Pigment Dispersion, C.I. I. Pigment Blue 15:3 (trade name: Chromofine Blue, manufactured by Dainichiseika Kogyo Co., Ltd.) was added to 20 g of C.I. I. Pigment Yellow 74 (trade name: Fast Yellow 531, manufactured by Dainichiseika Kogyo Co., Ltd.) was changed to 20 g, in the same manner as in Pigment Dispersion Production Example 1, to obtain a yellow pigment dispersion having a pigment concentration of 15% by mass. was made.

(Production Example 4 of Pigment Dispersion)
<Preparation of black pigment dispersion>
In Production Example 1 of Pigment Dispersion, C.I. I. Pigment Blue 15:3 (trade name: Chromo Fine Blue, manufactured by Dainichiseika Kogyo Co., Ltd.) was changed to 20 g of carbon black (NIPEX160, manufactured by degussa) in the same manner as in Pigment Dispersion Production Example 1. A black pigment dispersion having a pigment concentration of 15% by mass was prepared.

(Example 1)
<Production of ink set 1>
Ink Set 1 was prepared by combining Ink 1 containing a cyan pigment, Ink 1 containing a magenta pigment, Ink 1 containing a yellow pigment, and Ink 1 containing a black pigment, which were prepared as follows.

-Preparation of Ink Containing Cyan Pigment-
Cyan pigment dispersion 6.7% by mass, 1,3-butanediol (trade name: 1,3-butanediol, manufactured by Daicel Chemical Industries, Ltd.) 20% by mass, 3-methoxy-N,N-dimethylpropionamide (product Name: Equamid M-100, manufactured by Idemitsu Kosan Co., Ltd.) 10% by mass, diethylene glycol diethyl ether (trade name: Hisolve EDE, manufactured by Toho Chemical Industry Co., Ltd.) 5% by mass, triethylene glycol butyl methyl ether (trade name: Hisolve BTM , manufactured by Toho Chemical Industry Co., Ltd.) 5% by mass, polycarbonate urethane resin particle liquid (Takelac W6110, manufactured by Mitsui Chemicals, Inc., solid content concentration: 30% by mass) 10% by mass, siloxane compound (trade name: FZ2110, Toray Dow Co., Ltd., active ingredient concentration 100% by mass) 1% by mass, and the remaining amount of ion-exchanged water is added so that the total is 100% by mass, mixed and stirred, and then a membrane filter with an average pore size of 0.8 μm (trade name : DISMIC-25cs, manufactured by Advantech) to obtain Ink 1 containing a cyan pigment.

-Preparation of Ink Containing Magenta Pigment-
In the preparation of the ink containing the cyan pigment, the magenta pigment was prepared in the same manner as in the preparation of the ink containing the cyan pigment, except that the cyan pigment dispersion of 6.7% by mass was changed to the magenta pigment dispersion of 20.0% by mass. Ink 1 containing pigment was obtained.

-Preparation of ink containing yellow pigment-
In the preparation of the ink containing the cyan pigment, yellow was prepared in the same manner as in the preparation of the ink containing the cyan pigment, except that the 6.7% by weight of the cyan pigment dispersion was changed to 13.3% by weight of the yellow pigment dispersion. Ink 1 containing pigment was obtained.

-Preparation of Ink Containing Black Pigment-
In the preparation of the ink containing the cyan pigment, black was prepared in the same manner as in the preparation of the ink containing the cyan pigment, except that the 6.7% by weight of the cyan pigment dispersion was changed to 20.0% by weight of the black pigment dispersion. Ink 1 containing pigment was obtained.

(Examples 2 to 23 and Comparative Examples 1 to 6)
-Preparation of ink sets 2 to 29-
Tables 1 to 15 show the compositions and contents of Ink 1 containing a cyan pigment, Ink 1 containing a magenta pigment, Ink 1 containing a yellow pigment, and Ink 1 containing a black pigment in Example 1. Ink sets 2 to 29 of Examples 2 to 23 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1, except that the composition and content were changed. In Examples 18 and 19, acrylic resin emulsion (Boncoat CF-6140, manufactured by DIC Corporation, solid concentration: 48% by mass) was used.

<Image formation>
Using each of the obtained ink sets, polyvinyl chloride (PVC) (trade name: GIY-11Z5) was printed as shown in Tables 1 to 15 by the printing apparatus shown in FIG. , Lintec Co., Ltd.) and cloth (trade name: SS8000, Seiren Co., Ltd.), and printing was performed at a printing speed of 25 m ² /h.
In the liquid ejection unit shown in FIG. 2, the ink containing the black pigment of each ink set is used for "NK", "NC", "NM", and "NY" of the first nozzle group 20a to the third nozzle group 20c. , “Ink containing cyan pigment”, “Ink containing magenta pigment”, and “Ink containing yellow pigment” were used.
Next, the "color unevenness of the image" was evaluated as follows for each of the created images. The results are shown in Tables 1 to 15.

<Color unevenness of image>
The output image was a 4C composite image in which the gradation was changed from 100% solid chart to 0%. The 4C composite image was visually observed, and color unevenness of the image was evaluated based on the following criteria. In addition, 2 or more is an actual usable level.
[Evaluation criteria]
5: Color unevenness is not recognized at a distance of less than 30 cm from the image 4: Color unevenness is not recognized at a distance of 30 cm or more and less than 1 m from the image 3: Color unevenness is not recognized at a distance of 1 m or more and less than 2 m from the image 2: From the image Color unevenness is not recognized at a distance of 2m or more and less than 3m 1: Color unevenness is visible at a distance of 3m or more from the image

Embodiments of the present invention are, for example, as follows.
<1> An ink set containing an ink containing a black pigment, an ink containing a cyan pigment, an ink containing a magenta pigment, and an ink containing a yellow pigment,
An ink set characterized by satisfying the following formulas (1) and (2).
Black pigment content>Yellow pigment content>Cyan pigment content Formula (1)
Magenta pigment content>Yellow pigment content>Cyan pigment content Formula (2)
<2> The ink set according to <1>, satisfying the following formula: content of black pigment=content of magenta pigment.
<3> The ink set according to any one of <1> and <2>, wherein the black pigment content and the magenta pigment content are 2% by mass or more and 4% by mass or less.
<4> The difference (CB) between the magenta pigment content C and the cyan pigment content B is 0.8% by mass or more and 3% by mass or less in absolute value of <1> to <3> The ink set according to any one of the above.
<5> The ink set according to any one of <1> to <4>, wherein each ink of the ink set contains water, an organic solvent, and a resin.
<6> The ink set according to <5>, wherein the resin contains a urethane resin.
<7> The ink set according to any one of <5> to <6>, wherein each ink of the ink set further contains a surfactant.
<8> The ink set according to any one of <1> to <7>, which is used for a non-absorbent or low-absorbent recording medium.
<9> An ink set for use in a printing apparatus having an ejection means having four or more nozzle rows in which a plurality of nozzle holes for ejecting ink are arranged in a sub-scanning direction perpendicular to the main scanning direction,
An ink containing a black pigment, an ink containing a cyan pigment, an ink containing a magenta pigment, and an ink containing a yellow pigment,
An ink set characterized by satisfying the following formulas (1) and (2).
Black pigment content>Yellow pigment content>Cyan pigment content Formula (1)
Magenta pigment content>Yellow pigment content>Cyan pigment content Formula (2)
<10> The ink set according to <9>, satisfying the following formula: content of black pigment=content of magenta pigment.
<11> The ink set according to any one of <9> to <10>, wherein the black pigment content and the magenta pigment content are 2% by mass or more and 4% by mass or less.
<12> The above <9> to <11>, wherein the absolute value of the difference (CB) between the magenta pigment content C and the cyan pigment content B is 0.8% by mass or more and 3% by mass or less. The ink set according to any one of the above.
<13> The ink set according to any one of <9> to <12>, wherein each ink of the ink set contains water, an organic solvent, and a resin.
<14> The ink set according to <13>, wherein the resin contains a urethane resin.
<15> The ink set according to any one of <13> to <14>, wherein each ink of the ink set further contains a surfactant.
<16> The ink set according to any one of <9> to <15>, which is used for a non-absorbent or low-absorbent recording medium.
<17> Sub nozzle holes for ejecting at least one of a black pigment-containing ink, a cyan pigment-containing ink, a magenta pigment-containing ink, and a yellow pigment-containing ink are positioned perpendicular to the main scanning direction. A printing apparatus comprising an ejection means having four or more nozzle rows arranged in a scanning direction,
A printing apparatus, wherein the ink is each ink in the ink set according to any one of <1> to <8>.
<18> The printing apparatus according to <17>, wherein the ejection means has eight or more nozzle rows in which a plurality of nozzle holes through which ink is ejected are arranged in a sub-scanning direction orthogonal to a main scanning direction.
<19> Nozzle holes for ejecting at least one of ink containing a black pigment, ink containing a cyan pigment, ink containing a magenta pigment, and ink containing a yellow pigment are positioned perpendicular to the main scanning direction. A printing method using a printing apparatus having an ejection means having four or more nozzle rows arranged in a scanning direction,
A printing method, wherein the ink is each ink in the ink set according to any one of <1> to <8>.

According to the ink set described in any one of <1> to <16>, the printing apparatus described in any one of <17> to <18>, and the printing method described in <19>, various conventional The problem can be solved and the object of the present invention can be achieved.

Reference Signs List 1 inkjet recording apparatus 10 control unit 20 recording head 20a, 20b, 20c nozzle group

JP 2004-314352 A JP 2014-205767 A

Claims (12)

An ink set for use in a printing apparatus having ejection means having four or more nozzle rows in which a plurality of nozzle holes for ejecting ink are arranged in a sub-scanning direction perpendicular to the main scanning direction,
An ink containing a black pigment, an ink containing a cyan pigment, an ink containing a magenta pigment, and an ink containing a yellow pigment ,
satisfies the following formula: black pigment content = magenta pigment content,
The black pigment content and the magenta pigment content are 2% by mass or more and 4% by mass or less,
An ink set characterized by satisfying the following formulas (1) and (2).
Black pigment content>Yellow pigment content>Cyan pigment content Formula (1)
Magenta pigment content>Yellow pigment content>Cyan pigment content Formula (2) 2. The ink set according to claim 1, wherein the absolute value of the difference (CB) between the magenta pigment content C and the cyan pigment content B is 0.8 mass % or more and 3 mass % or less. 3. The ink set according to claim 1, wherein each ink of said ink set contains water, an organic solvent, and a resin. 4. The ink set according to claim 3, wherein the resin contains urethane resin. 5. The ink set according to claim 3, wherein each ink of said ink set further contains a surfactant. 6. The ink set according to claim 5, wherein the surfactant is a siloxane compound. 7. The ink set according to any one of claims 3 to 6, wherein the organic solvent contains 1,3-butanediol, 3-methoxy-N,N-dimethylpropionamide, diethylene glycol diethyl ether, and triethylene glycol butyl methyl ether. . 8. The ink set according to any one of claims 1 to 7, which is used for non-absorbent or low-absorbent recording media. 9. The ink set according to any one of claims 1 to 8, wherein the ejection means has eight or more nozzle rows in which a plurality of nozzle holes through which ink is ejected are arranged in a sub-scanning direction perpendicular to the main scanning direction. Nozzle holes for ejecting at least one kind of ink from among a black pigment-containing ink, a cyan pigment-containing ink, a magenta pigment-containing ink, and an ink containing a yellow pigment are arranged in the sub-scanning direction orthogonal to the main scanning direction. a discharge means having four or more nozzle rows arranged in a plurality ;
The ink is each ink in the ink set according to any one of claims 1 to 9 , and a tank containing each ink;
A printing device comprising : 11. The printing apparatus according to claim 10, wherein the ejection means has eight or more nozzle rows in which a plurality of nozzle holes through which ink is ejected are arranged in a sub-scanning direction perpendicular to the main scanning direction. Nozzle holes for ejecting at least one kind of ink from among a black pigment-containing ink, a cyan pigment-containing ink, a magenta pigment-containing ink, and an ink containing a yellow pigment are arranged in the sub-scanning direction orthogonal to the main scanning direction. A printing method using a printing device having ejection means having four or more nozzle rows arranged in a plurality,
A printing method, wherein the ink is each ink in the ink set according to any one of claims 1 to 9 .

Images