JP2020175663A - Inkjet recording method - Google Patents

Abstract

To provide an inkjet recording method capable of obtaining a good image without unevenness or color mixing without thermally deforming a low liquid-absorbing recording medium.SOLUTION: There is provided an inkjet recording method using an inkjet recording device having an inkjet head for discharging an aqueous ink onto a low liquid-absorbing recording medium to record an image on the recording medium, wherein the aqueous ink contains a colorant (A), a fixing aid polymer (B-2), an organic solvent (C) and water, the average particle diameter of fixing aid polymer (B-2) particles in the aqueous ink is 30 to 200 nm, the inkjet recording device has three or more aqueous inks having different static surface tensions, the recording medium is heated at 30 to 75°C and the aqueous inks are discharged onto the recording medium in the descending order of a static surface tension.SELECTED DRAWING: None

Description

The present invention relates to an inkjet recording method.

The inkjet recording method is a method in which ink droplets are directly ejected from a very fine nozzle onto a recording medium and adhered to obtain characters or images. This method is remarkably popular because it is easy to make full color, inexpensive, can use plain paper as a recording medium, and has many advantages such as non-contact with the printed matter.
On the other hand, in addition to printing on conventional plain paper and high-liquidity recording media called copy paper, low-liquidity coated paper such as offset coated paper, or polyvinyl chloride resin, polypropylene resin, and polyester resin. There has been a demand for printing on a recording medium for commercial printing using a non-liquid absorbing resin film such as.

When printing is performed on these low-liquid-absorbent and non-liquid-absorbent recording media by the inkjet recording method, it takes a long time to dry because the liquid components are slowly absorbed or not absorbed, and the scratch resistance at the initial stage of printing is deteriorated. It is known to be inferior.
Conventionally, solvent-based pigment inks using an organic solvent as a dispersion medium and UV-curable inks have been mainly used for printing on such low-liquidity and non-liquid-absorbent recording media. This utilizes the phenomenon that the organic solvent permeates into a low-liquidity, non-liquid-absorbent medium and swells the surface to immobilize the pigment in the recording medium, or on the recording medium after printing. This is because bleeding and scratch resistance can be improved by forming a strong resin film.
However, in these conventional inks, a large amount of organic solvent is diffused into the atmosphere when the ink dries, which affects the environment and the safety of the radical initiator and the monomer used in the UV curable ink. There is a problem that the concern may arise. For this reason, the development of water-based inks that have less burden on the work environment and the natural environment is currently underway.
On the other hand, most water-based inks have a problem that good image quality cannot be formed on a recording medium having low liquid absorption and non-liquid absorption.
In Patent Document 1, as a method of stabilizing the shape of ink dots to form a good image, a reaction solution containing a component that reacts with ink is applied to a recording medium, and then a plurality of types of ink having a higher surface tension are used in order. An image forming method for forming an image by applying ink is disclosed.
In Patent Document 2, as a method for forming a good image without uneven density or white spots on a non-absorbent recording medium, the ink evaporation rate and surface tension are within a specific range, and two or more kinds of organic solvents are contained. Disclosed is an inkjet recording method using an aqueous ink in which the sum of the hydrogen bond term and the polar term of the dissolution parameter is in a specific range and the content of the surfactant is less than the critical micelle concentration of the surfactant. ..

JP-A-2007-331171 Japanese Unexamined Patent Publication No. 2012-224658

Patent Document 1 is a technique of applying ink in descending order of surface tension to alleviate the phenomenon that the ink droplets applied first are pushed away by the ink droplets landed later and suppress the disorder of the shape of the ink dots. Is. However, in Patent Document 1, although the influence on the image due to the shape of the ink dots and the displacement of the landing position is evaluated, no concrete study has been made on the color mixing. Further, in paragraph [0013] of the same document, it is stated that color mixing is suppressed by the agglutination action using the reaction solution, and it is clearly stated that the image is severely deteriorated due to the color mixing when the reaction solution is not used.
Further, the inkjet recording method of Patent Document 2 has not sufficiently satisfied the problem of obtaining a good image without unevenness or color mixing on a non-liquid absorbing recording medium.
An object of the present invention is to provide an inkjet recording method capable of obtaining a good image without unevenness or color mixing without thermally deforming a low liquid absorption recording medium regardless of the presence or absence of agglutination action.

In the method of inkjet recording on a low liquid absorption recording medium, the present inventors heat the recording medium to 30 to 75 ° C. and use two or more water-based inks having different static surface tensions with high static surface tensions. It has been found that the above problems can be solved by discharging in order.
That is, the present invention is an inkjet recording method for recording on a recording medium using an inkjet recording device including an inkjet head that ejects water-based ink onto a low-liquidity recording medium, wherein the water-based ink is a colorant (colorant. A), a fixing aid polymer (B-2), an organic solvent (C), and water are contained, and the average particle size of the fixing aid polymer (B-2) particles in the water-based ink is 30 nm or more and 200 nm or less. The inkjet recording device is provided with three or more types of water-based inks having different static surface tensions, the recording medium is heated to 30 to 75 ° C., and the recording medium is made of water-based inks having a high static surface tension. The present invention relates to an inkjet recording method in which ink is ejected in order.

According to the present invention, it is possible to provide an inkjet recording method capable of obtaining a good image without unevenness or color mixing without thermally deforming a low liquid absorption recording medium.

It is a figure which shows the print pattern used at the time of print evaluation in an Example.

[Inkjet recording method]
The inkjet recording method of the present invention uses an inkjet recording device including an inkjet head that ejects water-based ink (hereinafter, also simply referred to as “ink”) onto a low-liquidity recording medium (hereinafter, also simply referred to as “recording medium”). This is an inkjet recording method for recording on the recording medium.
The water-based ink contains a colorant (A), a fixing aid polymer (B-2), an organic solvent (C), and water.
The average particle size of the fixing aid polymer (B-2) particles in the water-based ink is 30 nm or more and 200 nm or less.
The inkjet recording device includes three or more types of water-based inks having different static surface tensions.
The recording medium is heated to 30-75 ° C.
It is characterized in that the water-based ink having the highest static surface tension is sequentially ejected to the recording medium.
In the present specification, "recording" is a concept including printing and printing for recording characters and images, and "recorded matter" is a concept including printed matter and printed matter on which characters and images are recorded. is there.
Further, "low liquid absorption" is a concept including low liquid absorption and non-liquid absorption of water and / or ink, and low liquid absorption can be evaluated by the water absorption of pure water. More specifically, the amount of water absorption of the recording medium at a contact time of 100 msec between the recording medium and pure water is 0 g / m ² or more and 10 g / m ² or less, preferably 0 g / m ² or more and 6 g / m ² or less. It means that there is. The water absorption amount is measured by the method described in Examples.
Further, "water-based" means that water occupies the largest proportion of the medium contained in the ink, and the medium may be only water, and water and one or more organic solvents are used. The case of the mixed solvent of is also included.

According to the inkjet recording method of the present invention, it is possible to obtain a good image without unevenness or color mixing without thermally deforming the low liquid absorption recording medium. The reason is not clear, but it can be considered as follows.
When the low liquid absorption recording medium is heated in the recording step as in the present invention, the ink droplets landed first are dried and concentrated until the next ink droplets of another color land. When the ink is dried and concentrated, the composition of the water-based ink changes significantly because the water evaporates prior to the evaporation of the solvent. Due to this change in ink composition, the static surface tension of the ink gradually decreases. Therefore, when the next non-concentrated ink lands adjacent to the previously landed ink, the ink droplets having different static surface tensions come into contact with each other. When droplets having different static surface tensions come into contact with each other, wetting occurs at the interface, resulting in color mixing. Therefore, if the static surface tension of the subsequent ink is lower than that of the original ink in advance, it is possible to reduce the difference in static surface tension of the ink due to drying and concentration. As described above, it is considered that the present invention can suppress unevenness and color mixing by reducing the difference in static surface tension of each color ink in the heat-drying process.
Further, by using an organic solvent containing glycol ether as the organic solvent (C) and further containing a silicone-based surfactant as the surfactant (D), if necessary, non-liquid absorbing recording can be performed by an inkjet recording method. It is considered that the image uniformity due to the spread of dots when printed on a medium is further improved, and a good image without unevenness can be obtained.

<Water-based ink>
The water-based ink used in the present invention contains a colorant (A), an organic solvent (C), and water.
<Colorant (A)>
As the colorant (A) used for the water-based ink, either a pigment or a dye can be used, but the pigment is preferable from the viewpoint of imparting weather resistance and water resistance to the recorded material.
The pigment may be either an inorganic pigment or an organic pigment. In addition, if necessary, they can be used in combination with extender pigments.
Examples of the inorganic pigment include carbon black, metal oxide, metal sulfide, metal chloride and the like. Among these, carbon black is particularly preferable for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Further, in the white ink, metal oxides such as titanium oxide, zinc oxide, silica, alumina and magnesium oxide can be mentioned, and titanium oxide is preferable.
Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments and the like. The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred chromatic organic pigments include C.I. I. Pigment Yellow, C.I. I. Pigment Red, C.I. I. Pigment Orange, C.I. I. Pigment Violet, C.I. I. Pigment Blue and C.I. I. One or more product numbers selected from Pigment Green can be mentioned.
The above pigments and dyes can be used alone or in admixture of two or more.

The pigment used in the water-based ink can be used in one or more forms selected from a self-dispersing pigment and particles in which the pigment is dispersed with a polymer (B).
The polymer (B) can be used as a pigment-dispersed polymer (B-1) for dispersing the pigment and a fixing aid polymer (B-2) for improving the fixability of the image, and these can be used in combination. You can also do it.
As for the form of the pigment, it is more preferable that the pigment is contained in the water-based ink as particles of the water-insoluble polymer (BX) containing the pigment from the viewpoint of obtaining a good image without unevenness or color mixing.

[Autocovariant pigment]
The self-dispersing pigment is an alkandiyl having one or more hydrophilic functional groups (anionic hydrophilic groups such as a carboxy group or cationic hydrophilic groups such as a quaternary ammonium group) directly or having 1 to 12 carbon atoms. It means a pigment that can be dispersed in an aqueous medium without using a surfactant or a resin by binding to the surface of the pigment via another atomic group such as a group.
Examples of commercially available self-dispersing pigments include the CAB-O-JET series manufactured by Cabot Japan Co., Ltd. The self-dispersing pigment is preferably used as a pigment aqueous dispersion dispersed in water.

[Particles in which the pigment is dispersed with the polymer (B)]
The particles in which the pigment is dispersed in the polymer (B) are, for example, 1) particles in which the pigment and the polymer are kneaded and the kneaded product dispersed in a medium such as water, and 2) particles in which the pigment and the polymer are dispersed in a medium such as water. Particles in which the pigment is dispersed in a medium such as water by stirring in 3) The polymer raw material is polymerized in a state where the polymer raw material and the pigment are mechanically dispersed, and the pigment becomes a medium such as water by the obtained polymer. Examples include particles dispersed in the polymer.
Further, from the viewpoint of improving the storage stability in the water-based ink, a cross-linking agent may be added to the particles in which these pigments are dispersed with the polymer to cross-link the polymer.

[Polymer (B)]
Examples of the polymer (B) include condensed resins such as polyurethane and polyester, acrylic resins, styrene resins, styrene-acrylic resins, butadiene resins, styrene-butadiene resins, vinyl chloride resins, and vinyl acetate resins. And vinyl-based polymers such as acrylic silicone-based resins are mentioned, but vinyl-based polymers are preferable.
The weight average molecular weight of the polymer (B) is preferably 10,000 or more, more preferably 20,000 or more, still more preferably 30,000 or more, from the viewpoint of improving the dispersibility of the pigment and the fixing property of the obtained image. , More preferably 40,000 or more, and preferably 2.5 million or less, more preferably 1 million or less.

(Pigment dispersion polymer (B-1))
Examples of the pigment-dispersed polymer (B-1) include condensed resins such as polyester and polyurethane, vinyl-based polymers, and the like. From the viewpoint of pigment dispersion stability, vinyl monomers (vinyl compounds, vinylidene compounds, vinylene) are used. A vinyl-based polymer obtained by addition polymerization of the compound) is preferable. As the pigment dispersion polymer (B-1), one synthesized appropriately may be used, or a commercially available product may be used.
The weight average molecular weight of the pigment-dispersed polymer (B-1) is preferably 20,000 or more, more preferably 30,000 or more, still more preferably 40,000 or more, and preferably 40,000 or more, from the viewpoint of improving the dispersibility of the pigment. It is 500,000 or less, more preferably 300,000 or less, still more preferably 200,000 or less.
Examples of commercially available vinyl polymers include polyacrylic acids such as Aron AC-10SL (manufactured by Toagosei Corporation); John Krill 67, 611, 678, 680, 690, 819 (BASF Japan Ltd.). Styrene-acrylic resin and the like.

[Fixing aid polymer (B-2)]
The fixing aid polymer (B-2) is preferably used as pigment-free polymer particles. The dispersion of the fixing aid polymer (B-2) is formed on a recording medium to improve the fixability of the ink.
Examples of the fixing aid polymer (B-2) include condensation resins such as polyurethane and polyester, acrylic resins, styrene resins, styrene-acrylic resins, butadiene resins, styrene-butadiene resins, and vinyl chloride resins. Examples thereof include vinyl polymers such as vinyl acetate resins and acrylic silicone resins. Among these, an acrylic resin is preferable from the viewpoint of accelerating the drying property on the recording medium and improving the fixability of the image.
Further, the fixing aid polymer (B-2) is preferably used as a dispersion liquid containing polymer particles from the viewpoint of improving the productivity of the water-based ink. As the fixing aid polymer (B-2), for example, one produced by an emulsion polymerization method or the like may be used, or a commercially available product may be used.

Examples of commercially available fixing aid polymers (B-2) include Neocryl A1127 (manufactured by DSM NeoResins, anionic self-crosslinked water-based acrylic resin); acrylic resin such as John Krill 390 (manufactured by BASF Japan Ltd.); WBR- Urethane resins such as 2018, WBR-2000U (manufactured by Taisei Fine Chemical Co., Ltd.); styrene-butadiene resins such as SR-100, 102 (manufactured by Nippon A & L Inc.); John Krill 7100, 7600, 537J, 538J, Examples thereof include styrene-acrylic resins such as John Krill PDX-7164 (manufactured by BASF Japan Co., Ltd.); vinyl chloride resins such as Viniblanc 700 and Viniblanc 701 (manufactured by Nisshin Chemical Industry Co., Ltd.).
Examples of the form of the fixing aid polymer (B-2) include particles dispersed in water.

From the viewpoint of fixability, the weight average molecular weight of the fixing aid polymer (B-2) is preferably 10,000 or more, more preferably 20,000 or more, further preferably 30,000 or more, and preferably 2.5 million or less. , More preferably 1 million or less.
The average particle size of the fixing aid polymer (B-2) particles in the dispersion containing the fixing aid polymer (B-2) particles or in the ink is preferably 10 nm or more from the viewpoint of the storage stability of the ink. It is more preferably 30 nm or more, further preferably 50 nm or more, and preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less, still more preferably 130 nm or less.

<Water-insoluble polymer (BX)>
The water-insoluble polymer (BX) is preferably used as particles of the water-insoluble polymer containing a pigment (hereinafter, also referred to as “pigment-containing polymer particles”) from the viewpoint of obtaining a good image without unevenness or color mixing. Here, "water-insoluble" means that the dissolved amount of a polymer that has reached a constant weight after drying is 10 g or less, preferably 5 g or less, and more preferably 1 g or less when dissolved in 100 g of water at 25 ° C. means. When the water-insoluble polymer (BX) is an anionic polymer, it is the amount of dissolution when the anionic group of the polymer is 100% neutralized with NaOH.
As the water-insoluble polymer (BX), a vinyl-based polymer obtained by addition polymerization of a vinyl monomer is preferable from the viewpoint of improving the storage stability of the ink. As the vinyl-based polymer, a vinyl-based polymer obtained by copolymerizing a monomer mixture containing (b-1) an ionic monomer and (b-2) a hydrophobic monomer is preferable. This vinyl-based polymer has a structural unit derived from the component (b-1) and a structural unit derived from the component (b-2). Among them, those further containing the structural unit derived from (b-3) macromonomer are preferable.

Examples of the (b-1) ionic monomer include an anionic monomer and a cationic monomer, and an anionic monomer is preferable. Examples of the anionic monomer include a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer.
Examples of the carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and 2-methacryloyloxymethylsuccinic acid. Among the above, a carboxylic acid monomer is preferable, and acrylic acid and methacrylic acid are more preferable, from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink.

Examples of the hydrophobic monomer (b-2) include alkyl (meth) acrylic acid esters and aromatic group-containing monomers.
As the alkyl (meth) acrylic acid ester, those having an alkyl group having 1 to 22 carbon atoms are preferable, and for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, etc. Examples thereof include amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, and (iso) stearyl (meth) acrylate. ..
As the aromatic group-containing monomer, a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, which may have a substituent containing a heteroatom, is preferable, and a styrene-based monomer and an aromatic group-containing (meth) acrylic are preferable. Acid esters are more preferred.
As the styrene-based monomer, styrene, 2-methylstyrene, and divinylbenzene are preferable, and styrene is more preferable. As the aromatic group-containing (meth) acrylic acid ester, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate and the like are preferable, and benzyl (meth) acrylate is more preferable.

(B-3) The macromonomer is a compound having a polymerizable functional group at one end and having a number average molecular weight of 500 or more and 100,000 or less. As the polymerizable functional group present at one end, an acryloyloxy group or a methacryloyloxy group is preferable.
(B-3) The number average molecular weight of the macromonomer is preferably 1,000 or more and 10,000 or less. The number average molecular weight is measured by gel permeation chromatography using polystyrene as a standard substance.
(B-3) As the macromonomer, an aromatic group-containing monomer-based macromonomer and a silicone-based macromonomer are preferable from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink, and the aromatic group-containing monomer-based macromonomer is preferable. Monomers are more preferred.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomer described in (b-2) Hydrophobic Monomer, and styrene and benzyl (meth) acrylate are preferable. Styrene is more preferred.
Specific examples of the styrene-based macromonomer include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toagosei Co., Ltd.) and the like.

The (b-4) nonionic monomer is preferably used as a monomer component from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink.
As the component (b-4), 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (n = 2 to 30, n indicates the average number of moles of the oxyalkylene group added. (Same as above) Polyalkylene glycol (meth) acrylate such as (meth) acrylate and polyethylene glycol (n = 2 to 30) (meth) acrylate, alkoxy polyalkylene glycol such as methoxypolyethylene glycol (n = 1 to 30) (meth) acrylate Examples thereof include (meth) acrylate and phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1 to 30, ethylene glycol: n = 1 to 29) (meth) acrylate.
Specific examples of commercially available (b-4) components include Shin Nakamura Chemical Industry Co., Ltd.'s NK Ester M-20G, 40G, 90G, 230G, etc., and NOF Corporation's Blemmer PE-90. , 200, 350, etc., PME-100, 200, 400, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, etc., 50PEP-300, 50POEP-800B, 43PAPE -600B and the like can be mentioned.
The above components (b-1) to (b-4) can be used alone or in combination of two or more.

The content of the structural units derived from the components (b-1) to (b-4) in the water-insoluble polymer (BX) is as follows from the viewpoint of the dispersion stability of the pigment-containing polymer particles.
The content of the component (b-1) is preferably 3% by mass or more, more preferably 5% by mass or more, further preferably 7% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass. % Or less, more preferably 20% by mass or less.
The content of the component (b-2) is preferably 25% by mass or more, more preferably 30% by mass or more, further preferably 35% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass. % Or less, more preferably 50% by mass or less.
The content of the component (b-3) is 0% by mass or more, preferably 5% by mass or more, more preferably 8% by mass or more, further preferably 10% by mass or more, and preferably 30% by mass or less. It is more preferably 25% by mass or less, still more preferably 20% by mass or less.
The content of the component (b-4) is 0% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 50% by mass or less. It is more preferably 45% by mass or less, still more preferably 40% by mass or less.

[Manufacturing of water-insoluble polymer (BX)]
The water-insoluble polymer (BX) can be obtained by copolymerizing with a known polymerization method, for example, a solution polymerization method. The water-insoluble polymer (BX) is used in step I, which will be described later, without removing the solvent used in the polymerization reaction from the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing polymer particles, which will be described later. Since it is used as an organic solvent, it is preferably used as it is as a water-insoluble polymer solution.

The weight average molecular weight of the water-insoluble polymer (BX) is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 20,000 or more, and from the viewpoint of obtaining a good image without unevenness or color mixing. It is preferably 500,000 or less, more preferably 400,000 or less, still more preferably 300,000 or less, still more preferably 200,000 or less.
The present form of the water-insoluble polymer (BX) in the water-based ink is from the particle form in which the polymer encapsulates (encapsulates) the pigment, the particle form in which the pigment is uniformly dispersed in the polymer, and the particle surface of the polymer. The particle form in which the pigment is exposed, the form in which the polymer is adsorbed on the pigment, the form in which the polymer is not adsorbed on the pigment, and the like are included, and a form in which these are mixed is also included. From the viewpoint of the dispersion stability of the pigment, the form of the pigment-containing polymer particles is preferable in the present invention, and the pigment-encapsulated form in which the water-insoluble polymer (BX) contains the pigment is more preferable.

[Manufacture of Pigment-Containing Water-Insoluble Polymer (BX) Particles (Pigment-Containing Polymer Particles)]
The pigment-containing polymer particles can be efficiently produced as an aqueous dispersion by a method having the following steps I, II, and if necessary, further step III.
Step I: A mixture containing a water-insoluble polymer (BX), an organic solvent, a pigment, and water (hereinafter, also referred to as "pigment mixture") is dispersed to obtain a dispersion of pigment-containing polymer particles. Step II: Step III: Water obtained in Step II by removing the organic solvent from the dispersion obtained in Step I to obtain an aqueous dispersion of pigment-containing polymer particles (hereinafter, also referred to as “pigment aqueous dispersion”). Step of mixing the dispersion and the cross-linking agent and cross-linking to obtain an aqueous dispersion

(Step I)
In step I, first, the water-insoluble polymer (BX) is dissolved in an organic solvent, then the pigment, water, and if necessary, a neutralizing agent, a surfactant, etc. are added to the obtained organic solvent solution and mixed. However, a method of obtaining an oil-in-water type dispersion is preferable.
The organic solvent that dissolves the water-insoluble polymer (BX) is not limited, but when the water-insoluble polymer is synthesized by the solution polymerization method, the solvent used in the polymerization may be used as it is.
When the water-insoluble polymer (BX) is an anionic polymer, a neutralizing agent may be used to neutralize the anionic groups in the water-insoluble polymer. Examples of the neutralizing agent include alkali metal hydroxides, ammonia, organic amines and the like.
The dispersion treatment method in step I is not particularly limited, but preferably, after the pigment mixture is pre-dispersed, shear stress is further applied to perform the main dispersion, and the average particle size of the pigment particles is controlled to be a desired particle size. It is preferable to do so. Examples of the pre-dispersion device include commonly used mixing and stirring devices such as anchor blades and discharge blades, but a high-speed stirring and mixing device is preferable.
Examples of this disperser include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidic (manufactured by Microfluidic), and a media disperser such as a paint shaker and a bead mill. A high-pressure homogenizer is preferable from the viewpoint of When the main dispersion is performed using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the processing pressure and the number of passes.

(Step II)
In step II, the organic solvent can be removed from the dispersion obtained in step I by a known method to obtain a pigment aqueous dispersion. It is preferable that the organic solvent in the obtained aqueous pigment dispersion is substantially removed, but a small amount may remain as long as the object of the present invention is not impaired.
The obtained pigment aqueous dispersion is one in which solid water-insoluble polymer (BX) particles containing a pigment are dispersed in a medium containing water as a main medium. Here, the form of the pigment-containing polymer particles is not particularly limited, but as described above, the pigment-containing state in which the pigment is contained is more preferable.

(Step III)
Although step III is an arbitrary step, it is preferable to carry out step III from the viewpoint of storage stability of the pigment aqueous dispersion and the ink.
Here, the cross-linking agent is preferably a compound having a functional group that reacts with the anionic group when the water-insoluble polymer (BX) is an anionic water-insoluble polymer having an anionic group, and the functional group is contained in the molecule. A compound having 2 or more, preferably 2 to 6 is more preferable.
Preferable examples of the cross-linking agent include a compound having two or more epoxy groups in the molecule, a compound having two or more oxazoline groups in the molecule, and a compound having two or more isocyanate groups in the molecule. In the above, a compound having two or more epoxy groups in the molecule is preferable, and trimethylolpropane polyglycidyl ether is more preferable.

The solid content concentration of the obtained aqueous pigment dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 35, from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion. It is mass% or less, more preferably 30 mass% or less. The solid content concentration of the aqueous pigment dispersion is measured by the method described in Examples.
The average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion is preferably 40 nm or more, more preferably 60 nm or more, still more preferably 80 nm or more, and further, from the viewpoint of reducing coarse particles and improving continuous ejection properties. It is preferably 85 nm or more, and preferably 150 nm or less, more preferably 130 nm or less, still more preferably 125 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in Examples.

<Organic solvent (C)>
The organic solvent (C) preferably has a boiling point of 90 ° C. or higher and lower than 250 ° C. from the viewpoint of obtaining a good image without unevenness or color mixing. The boiling point of the organic solvent (C) is preferably 130 ° C. or higher, more preferably 140 ° C. or higher, further preferably 150 ° C. or higher, and preferably 245 ° C. or lower, preferably 240 ° C. or lower, preferably 235 ° C. or lower. Is.
Preferable examples of the organic solvent (C) include polyhydric alcohol (c-1) and glycol ether (c-2).

(Multivalent alcohol (c-1))
Examples of the polyhydric alcohol (c-1) include 1,2-alkanediol such as ethylene glycol, propylene glycol, 1,2-butanediol, 1,2-pentanediol and 1,2-hexanediol, diethylene glycol and polyethylene glycol. , Dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, 2-methyl-2, Examples thereof include 4-pentanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol and petriol.
Among these, from the viewpoint of improving the storage stability and continuous ejection property of the ink, the number of carbon atoms such as propylene glycol (boiling point 188 ° C.), diethylene glycol (boiling point 245 ° C.), 1,2-hexanediol (boiling point 223 ° C.) One or more selected from 2 or more and 6 or less alkane diols and polypropylene glycol having a molecular weight of 500 to 1000 is preferable, and from 1,2-alkane diols having 3 or more and 4 or less carbon atoms such as propylene glycol and diethylene glycol, and the polypropylene glycol. One or more selected are more preferable.

(Glycol ether (c-2))
Specific examples of the glycol ether (c-2) include alkylene glycol monoalkyl ether, alkylene glycol dialkyl ether, etc., from the viewpoint of improving continuous ejection property and obtaining a good image without unevenness or color mixture. Alkylene glycol monoalkyl ethers are preferred. The alkyl group of the alkylene glycol monoalkyl ether preferably has 1 or more carbon atoms, more preferably 2 or more carbon atoms, still more preferably 3 or more carbon atoms, and preferably 6 or less, more preferably 4 or less carbon atoms. The alkyl group of the alkylene glycol monoalkyl ether may be a straight chain or a branched chain.
Specific examples of the alkylene glycol monoalkyl ether include ethylene glycol ethyl ether, ethylene glycol isopropyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol isopropyl ether, diethylene glycol isobutyl ether, diethylene glycol butyl ether, and tri. Examples thereof include ethylene glycol methyl ether, dipropylene glycol butyl ether, dipropylene glycol methyl ether, and tripropylene glycol methyl ether.
Among these, ethylene glycol isopropyl ether (boiling point 144 ° C.), ethylene glycol propyl ether (boiling point 151 ° C.), diethylene glycol methyl ether (boiling point 194 ° C.), diethylene glycol isopropyl ether (boiling point 207 ° C.), diethylene glycol isobutyl ether (boiling point 230 ° C.) ), And one or more selected from diethylene glycol butyl ether (boiling point of 230 ° C.) are preferable, and one or more selected from ethylene glycol isopropyl ether, diethylene glycol isopropyl ether, and diethylene glycol isobutyl ether are more preferable.

(Other organic solvents)
In the present invention, in addition to the organic solvent (C), other alcohols usually blended in aqueous inks, nitrogen-containing heterocyclic compounds such as alkyl ethers, glycol ethers, and NMPs of the alcohols, amides, amines, and sulfur-containing compounds. It can contain compounds and the like.
For example, 1,6-hexanediol (boiling point 250 ° C.), triethylene glycol (boiling point 285 ° C.), tripropylene glycol (boiling point 273 ° C.), polypropylene glycol (boiling point 250 ° C. or higher), glycerin (boiling point 290 ° C.), etc. Can be used in combination with solvents below 250 ° C.

<Surfactant (D)>
The water-based ink used in the present invention preferably contains a surfactant (D) from the viewpoint of obtaining a good image without unevenness or color mixing, and the surfactant (D) is a silicone-based surfactant ( Those containing d-1) are preferable.
The silicone-based surfactant (d-1) can be appropriately selected depending on the intended purpose, but it suppresses an increase in ink viscosity, improves continuous ejection property, and produces a good recorded material without unevenness or color mixing. From the viewpoint of obtaining, a polyether-modified silicone-based surfactant is preferable.

(Polyether-modified silicone-based surfactant)
Since the polyether-modified silicone-based surfactant can suppress an increase in ink viscosity and color mixing between inks, it is considered to contribute to obtaining a good recorded material without unevenness or color mixing in high-speed printing. Be done.
The polyether-modified silicone-based surfactant has a structure in which the side chain and / or the hydrocarbon group at the terminal of the silicone oil is replaced with a polyether group. As the polyether group, a polyalkyleneoxy group in which a polyethyleneoxy group, a polypropyleneoxy group, an ethyleneoxy group (EO) and a propyleneoxy group (PO) are added in a block shape or at random is preferable, and a polyalkyleneoxy group is added to the silicone main chain. A compound in which an ether group is grafted, a compound in which a silicone and a polyether group are bonded in a block shape, and the like can be used.
The HLB value of the polyether-modified silicone-based surfactant is preferably 3.0 or more, more preferably 4.0 or more, still more preferably 4.5 or more, from the viewpoint of solubility in water-based ink. Here, the HLB value is a value indicating the affinity of the surfactant for water and oil, and can be obtained from the following formula by the Griffin method. In the following formula, examples of the "hydrophilic group contained in the surfactant" include a hydroxyl group and an ethyleneoxy group.
HLB = 20 × [(Molecular weight of hydrophilic group contained in surfactant) / (Molecular weight of surfactant)]
Specific examples of the polyether-modified silicone-based surfactant include the KF series manufactured by Shin-Etsu Chemical Co., Ltd., the Silface SAG manufactured by Shin-Etsu Chemical Co., Ltd., and the BYK series manufactured by Big Chemie Japan Co., Ltd.

(Other surfactants)
In the present invention, a surfactant other than the polyether-modified silicone-based surfactant can be used in combination. Among them, nonionic surfactants are preferable.
Examples of the nonionic surfactant include (1) polyoxyalkylene alkyl ethers and alkenyl ethers obtained by adding an alkylene oxide to an aliphatic or aromatic alcohol or polyhydric alcohol having 8 to 22 carbon atoms, and (2) carbon. An ester of an alcohol having a hydrocarbon group of 8 to 22 and a polyhydric fatty acid, (3) a polyoxyalkylene aliphatic amine having an alkyl group or an alkenyl group of 8 to 20 carbon atoms, and (4) 8 to 22 carbon atoms. Examples thereof include an ester compound of a higher fatty acid and a polyhydric alcohol, or a compound to which an alkylene oxide is added.
Examples of commercially available nonionic surfactants include the Surfinol series manufactured by Nissin Chemical Industry Co., Ltd., the acetylenol series manufactured by Kawaken Fine Chemical Co., Ltd., and Emargen 120 (polyoxyethylene lauryl ether) manufactured by Kao Corporation. Can be mentioned.

[Contents of each component of water-based ink, ink physical properties]
The water-based ink used in the present invention can be obtained by appropriately mixing and stirring the above components. The content and physical properties of each component of the obtained water-based ink are as follows.
(Content of pigment (A))
The content of the pigment (A) in the water-based ink is preferably 2.0% by mass or more, more preferably 4.0% by mass or more, still more preferably 6.0% by mass, from the viewpoint of improving the recording density of the water-based ink. % Or more. Further, from the viewpoint of lowering the ink viscosity at the time of solvent volatilization, improving continuous ejection property, and obtaining a good image without unevenness or color mixing, preferably 30.0% by mass or less, more preferably 20% by mass or less. It is more preferably 15% by mass or less, and even more preferably 10.0% by mass or less.

(Content of polymer (B))
The content of the polymer (B) in the water-based ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 3.0% by mass or more, from the viewpoint of fixability. Then, it is preferably 20% by mass or less, more preferably 13% by mass or less, and further preferably 8.0% by mass or less.
When the polymer (B) is used as the pigment-dispersed polymer (B-1), the content of the pigment-dispersed polymer (B-1) is preferably 0.01% by mass or more, more preferably 0, from the viewpoint of fixability. It is 05% by mass or more, more preferably 0.1% by mass or more, and preferably 10% by mass or less, more preferably 7.0% by mass or less, still more preferably 5.0% by mass or less.
When the polymer (B) is used as the fixing aid polymer (B-2), the content of the fixing aid polymer (B-2) is preferably 0.9% by mass or more from the viewpoint of ink fixability. It is preferably 1.0% by mass or more, more preferably 1.2% by mass or more, and preferably 10% by mass or less, more preferably 6.0% by mass or less, still more preferably 3.0% by mass or less. is there.
When particles of a water-insoluble polymer (BX) containing a pigment are used, the content of the polymer (B) in the water-based ink is the pigment dispersion polymer (B-1) of the pigment-containing polymer particles and the fixing aid polymer. It is a total amount including (B-2).

(Content of organic solvent (C))
The content of the organic solvent (C) in the water-based ink is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, from the viewpoint of improving the continuous ejection property of the ink. Then, it is preferably 45% by mass or less, more preferably 40% by mass or less, and further preferably 35% by mass or less.
The content of the polyhydric alcohol (c-1) in the water-based ink is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 15% by mass or more, from the viewpoint of improving the storage stability and continuous ejection property of the ink. It is 20% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, and further preferably 35% by mass or less.
The content of glycol ether (c-2) in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3 from the viewpoint of improving the storage stability and continuous ejection property of the ink. It is 5% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, and further preferably 8% by mass or less.
The water-based ink used in the present invention preferably has a high boiling point organic solvent having a boiling point of 250 ° C. or higher from the viewpoint of imparting appropriate drying properties in high-speed printing and obtaining a good image without unevenness or color mixing. It is 5% by mass or less, more preferably 4% by mass or less, still more preferably 3% by mass or less.

(Content of surfactant (D))
The content of the surfactant (D) in the water-based ink is preferably 0.1 from the viewpoint of suppressing an increase in ink viscosity, improving the continuous ejection property of the ink, and obtaining a good image without unevenness or color mixture. By mass or more, more preferably 0.2% by mass or more, further preferably 0.5% by mass or more, and preferably 5% by mass or less, more preferably 4% by mass or less, still more preferably 3% by mass. % Or less, more preferably 2.5% by mass or less.
From the same viewpoint as above, the content of the silicone-based surfactant (d-1) in the water-based ink is preferably 0.005% by mass or more, more preferably 0.03% by mass or more, still more preferably 0. It is 04% by mass or more, and preferably 0.5% by mass or less, more preferably 0.4% by mass or less, and further preferably 0.3% by mass or less.
From the same viewpoint as above, the content of the polyether-modified silicone-based surfactant in the water-based ink is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, still more preferably 0.03% by mass. % Or more, and preferably 0.5% by mass or less, more preferably 0.4% by mass or less, still more preferably 0.2% by mass or less.
From the same viewpoint as above, the content of the nonionic surfactant (d-2) in the water-based ink is preferably 0.1% by mass or more, more preferably 0.8% by mass or more, still more preferably 1. It is 5% by mass or more, and preferably 5% by mass or less, more preferably 3.5% by mass or less, still more preferably 2.5% by mass or less.

(Water content)
The content of water in the water-based ink is preferably 20% by mass or more, more preferably 30% by mass or more, from the viewpoint of improving the continuous ejection property and storage stability of the ink and obtaining a good image without unevenness or color mixing. It is more preferably 40% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less.
In addition to the above components, various additives such as moisturizing agents, wetting agents, penetrants, defoaming agents, preservatives, fungicides, and rust preventives, which are usually used, are added to the water-based ink used in the present invention. be able to.

<Physical properties of water-based ink>
In the inkjet recording method of the present invention, two or more kinds of inks selected from black ink, white ink, and chromatic ink, and water-based inks having different static surface tensions are used. The water-based ink is preferably used in an amount of 3 or more, more preferably 4 or more, and preferably 8 or less, preferably 7 or less. As a combination of a plurality of water-based inks, for example, four combinations of black ink, cyan ink, magenta ink and yellow ink, five combinations of black ink, cyan ink, magenta ink, yellow ink and white ink, black ink, 7 combinations of cyan ink, magenta ink, yellow ink, red ink, green ink and blue ink, 8 types of black ink, cyan ink, magenta ink, yellow ink, red ink, green ink, blue ink and white ink There are combinations.
The static surface tension of the water-based ink at 20 ° C. is preferably 22 mN / m or more, more preferably 24 mN / m or more, from the viewpoint of obtaining a good image without unevenness or color mixing and improving the ejection property of the water-based ink. It is more preferably 25 mN / m or more, and preferably 45 mN / m or less, more preferably 40 mN / m or less, still more preferably 35 mN / m or less.
The difference in static surface tension between the two or more inks is preferably 0.1 mN / m or more, more preferably 0.2 mN / m or more, still more preferably 0.2 mN / m or more, from the viewpoint of obtaining a good image without unevenness or color mixing. It is preferably 0.3 mN / m or more.
The static surface tension of the ink can be adjusted, for example, by selecting the type and content of the organic solvent (C) and the surfactant (D).

The average particle size of the particles contained in the water-based ink is preferably 40 nm or more, more preferably 60 nm or more, further preferably 80 nm or more, and preferably 250 nm or less, more preferably, from the viewpoint of storage stability and ejection property. Is 220 nm or less, more preferably 200 nm or less, and even more preferably 180 nm or less.
The average particle size and static surface tension are measured by the method described in Examples.
The viscosity of the water-based ink at 32 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, still more preferably 4.0 mPa · s or more, from the viewpoint of improving the continuous ejection property of the ink. And, preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, still more preferably 7.0 mPa · s or less.
The pH of the water-based ink is preferably 7.0 or more, more preferably 8.0 or more, still more preferably 8.5 or more, from the viewpoint of storage stability and the like, and from the viewpoint of obtaining a good recorded material without unevenness or color mixing. It is more preferably 8.7 or more, and preferably 11.0 or less, more preferably 10.0 or less from the viewpoint of member resistance and skin irritation.

<Inkjet recording method>
The inkjet recording method of the present invention is a method in which an inkjet recording device provided with an inkjet head for ejecting the above-mentioned water-based ink is used as a low-liquidity recording medium, and the inkjet recording device is a water-based device having a different static surface tension. This is an inkjet recording method in which two or more types of ink are provided, the recording medium is heated to 30 to 75 ° C., and water-based ink having the highest static surface tension is ejected to the recording medium in order.
As in the present invention, the difference in static surface tension of each color ink in the heating and drying process can be reduced by setting the static surface tension of the later ink to be lower than that of the first ink to be ejected. Therefore, it is considered that unevenness and color mixing can be suppressed.

(Low liquid absorption recording medium)
Examples of the low-liquidity recording medium used in the present invention include low-liquidity coated paper and resin film, which may be sheet-fed paper or roll-up paper, but from the viewpoint of productivity, a roll-shaped recording medium. Is preferable.
As coated paper, general-purpose glossy paper "OK Top Coat Plus" (manufactured by Oji Paper Co., Ltd., water absorption at a contact time of 100 msec (same below) 4.9 g / m ² ), multicolor foam gloss paper (Oji Paper Co., Ltd.) , Water absorption of 5.2 g / m ² ), UPM Finesse Gloss (made by UPM, water absorption of 3.1 g / m ² ) and the like.
Examples of the resin film include a transparent synthetic resin film, and examples thereof include a polyester film, a vinyl chloride film, a polypropylene film, a polyethylene film, and a nylon film. These films may be biaxially stretched films, uniaxially stretched films, and non-stretched films. Among these, a polyester film and a stretched polypropylene film are more preferable, and a polyester film such as a corona discharge-treated polyethylene terephthalate (PET) film and a stretched polypropylene film such as a corona discharge-treated biaxially stretched polypropylene (OPP) film are preferable. More preferable.
The thickness of the resin film is not particularly limited. A thin film having a thickness of less than 1 to 20 μm may be used, but from the viewpoint of suppressing poor appearance of the recording medium and availability, it is preferably 20 μm or more, more preferably 30 μm or more, still more preferably 35 μm or more, and preferably. Is 100 μm or less, more preferably 80 μm or less, still more preferably 75 μm or less.
Examples of commercially available transparent synthetic resin films include Lumirer T60 (manufactured by Toray Co., Ltd., PET), Taiko FE2001 (manufactured by Futamura Chemical Co., Ltd., corona discharge treatment PET), and Taiko FOR-AQ (manufactured by Futamura Chemical Co., Ltd., corona discharge). Processed OPP), PVC80BP (Lintec Co., Ltd., vinyl chloride), Kinas KEE70CA (Lintech Co., Ltd., polyethylene), YUPO SG90 PAT1 (Lintech Co., Ltd., PP), Bonnir RX (Kojin Film & Chemicals Co., Ltd.) , Nylon) and the like.

(Inkjet recording device)
The inkjet recording device used in the present invention includes two or more types of water-based inks. When the inkjet recording device includes a plurality of water-based inks, it means that the inkjet recording device has an ejection port of an inkjet head that ejects the plurality of each water-based ink. For example, when the inkjet recording device includes two types of water-based inks, it has an ejection port of an inkjet head that ejects each of the two types of water-based inks. In this case, the number of inkjet heads may be 1 or 2. The inkjet recording device is provided with two or more types of water-based inks, and preferably includes three or more types of water-based inks, more preferably four or more types, and water-based inks from the viewpoint of obtaining a good image without unevenness or color mixing. Is preferably 8 kinds or less, preferably 7 kinds or less.
The inkjet recording apparatus used in the present invention includes an inkjet head that ejects water-based ink to a recording medium that moves in the feed direction in order to heat the recording medium to 30 to 75 ° C., and a surface of the recording medium that faces the head. Is preferably provided with an underheater that heats the recording medium from the back surface.

(Inkjet head)
Examples of the inkjet head include a serial head method and a line head method, but the line head method is preferable. The line head method is a method in which the head is fixed, the recording medium is moved in the transport direction, ink droplets are ejected from the nozzle opening of the head in conjunction with this movement, and the ink droplets are attached to the recording medium. It can be recorded by the one-pass method.
The piezo method is preferable as the ink droplet ejection method. In the piezo method, a large number of nozzles communicate with each other in the pressure chamber, and the wall surface of the pressure chamber is vibrated by the piezo element to eject ink droplets from the nozzles. A thermal method can also be adopted.
The applied voltage of the recording head is preferably 5 V or more, more preferably 10 V or more, still more preferably 15 V or more, and preferably 40 V or less, more preferably 35 V or less, further, from the viewpoint of high-speed printing efficiency and the like. It is preferably 30 V or less.
The drive frequency is preferably 2 kHz or more, more preferably 5 kHz or more, still more preferably 8 kHz or more, and preferably 80 kHz or less, more preferably 70 kHz or less, still more preferably 60 kHz, from the viewpoint of high-speed printing efficiency and the like. It is as follows.

(Recording conditions, etc.)
From the viewpoint of maintaining the accuracy of the landing position of the ink droplets and improving the image quality, the amount of ink ejected droplets is preferably 0.5 pL or more, more preferably 1.0 pL or more, and further preferably 1. It is 5 pL or more, more preferably 1.8 pL or more, and preferably 20 pL or less, more preferably 15 pL or less, still more preferably 13 pL or less.
The recording head resolution is preferably 400 dpi (dots / inch) or more, more preferably 500 dpi or more, still more preferably 550 dpi or more.
The temperature inside the head during recording, preferably inside the line head, is preferably 20 ° C. or higher, more preferably 25 ° C. or higher, still more preferably 30 ° C. or higher, from the viewpoint of lowering the viscosity of the ink and improving the continuous ejection property. Yes, and preferably 45 ° C. or lower, more preferably 40 ° C. or lower, still more preferably 38 ° C. or lower.
The surface temperature of the recording medium facing the region where the recording head, preferably the line head ejects ink, is heated to 30 ° C. or higher from the viewpoint of obtaining a good recorded material without unevenness or color mixing, thereby causing thermal deformation of the recorded material. From the viewpoint of suppressing and suppressing the consumption of manufacturing energy, the temperature is set to 75 ° C. or lower. The temperature of the recording medium is preferably 35 ° C. or higher, more preferably 40 ° C. or higher, further preferably 45 ° C. or higher, and preferably 70 ° C. or lower, more preferably 65 ° C. or lower, still more preferably 60 ° C. or lower. Even more preferably, it is 55 ° C. or lower.
The temperature of the recording medium can be adjusted by adjusting the temperature of the underheater.
From the viewpoint of productivity, the recording speed is usually 5 m / min or more, preferably 10 m / min or more, more preferably 20 m / min or more, still more preferably 20 m / min or more, in terms of the transport speed in the direction in which the recording medium moves during recording. Is 30 m / min or more, and is preferably 75 m / min or less from the viewpoint of operability.
The amount of the water-based ink adhered to the recording medium is preferably 0.1 g / m ² or more, and preferably 25 g / m ² or less, as a solid content, from the viewpoint of improving the image quality of the recorded material and the recording speed. It is preferably 20 g / m ² or less.

(Under heater)
The underheater provided in the inkjet recording device is arranged on a surface opposite to the surface of the recording medium, which faces the recording head of the water-based ink, and heats the recording medium. The underheater can be, for example, a heater having a hot water type or a thermoelectric type stainless steel or ceramic plate. When there are a plurality of recording heads for ejecting a plurality of inks, the underheater is preferably arranged at a position facing each recording head.
The underheater is preferably 0.05 mm or more, more preferably 0.1 mm or more, still more preferably 0.2 mm or more, still more preferably 0.4 mm or more from the back surface of the recording medium at the time of printing. Then, it is preferably arranged at a position separated by 5.0 mm or less, more preferably 4.0 mm or less, further preferably 3.0 mm or less, still more preferably 2.0 mm or less, still more preferably 1.5 mm or less.
In the inkjet recording method of the present invention, a kind of ink is ejected to record an image, and even if the next ink is subsequently ejected, the droplets of each ink are not mixed with each other, so that a heater or the like is further used. It is also possible to provide a fixing / curing means for applying thermal energy.

Regarding the above-described embodiment, the present invention further discloses the following inkjet recording method.
<1> An inkjet recording method for recording on a recording medium using an inkjet recording device provided with an inkjet head that ejects water-based ink onto a low-liquidity recording medium.
The water-based ink contains a colorant (A), an organic solvent (C), and water.
The inkjet recording device includes two or more types of water-based inks having different static surface tensions.
The recording medium is heated to 30-75 ° C.
An inkjet recording method in which water-based ink having a higher static surface tension is sequentially ejected onto the recording medium.
<2> The inkjet recording method according to <1>, wherein the colorant (A) is contained in the water-based ink as water-insoluble polymer particles containing a pigment.
<3> The inkjet recording method according to <1> or <2> above, wherein the organic solvent (C) contains glycol ether (c-2).
<4> The inkjet recording method according to any one of <1> to <3> above, wherein the water-based ink further contains a polymer (B).
<5> The inkjet recording method according to any one of <1> to <4> above, wherein the water-based ink further contains a surfactant (D).
<6> The inkjet recording method according to <5> above, wherein the surfactant (D) contains a silicone-based surfactant (d-1).
<7> The inkjet recording method according to any one of <1> to <6> above, wherein the low liquid absorption recording medium is a polyester film that has undergone corona discharge treatment or a stretched polypropylene film that has undergone corona discharge treatment.
<8> The above <1> to <7, wherein the recording medium is heated by an inkjet head that ejects water-based ink onto the recording medium and an underheater provided on a surface opposite to the surface of the recording medium facing the head. > The inkjet recording method according to any one of.
<9> The inkjet recording method according to any one of <1> to <8>, wherein the recording speed is 5 m / min or more and 75 m / min or less in terms of the transport speed of the recording medium.
<10> The inkjet recording method according to any one of <1> to <9>, wherein the one-pass method is used for recording.

In the following production examples, examples and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The method for measuring each physical property is as follows.

(1) Measurement of weight average molecular weight of water-insoluble polymer Gel permeation using a solution prepared by dissolving polystyrene and lithium bromide in N, N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively, as an eluent. The molecular weight is known in advance as a standard substance by a chromatography method [GPC apparatus manufactured by Tosoh Corporation (HLC-8120 GPC), column manufactured by Tosoh Corporation (TSK-GEL, α-M x 2), flow velocity: 1 mL / min]. It was measured using the monodisperse polystyrene of.
(2) Measurement of solid content concentration of pigment aqueous dispersion Weigh 10.0 g of sodium sulfate homogenized in a desiccator into a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), and sample about 1. After adding 0 g and mixing, the mixture was accurately weighed, maintained at 105 ° C. for 2 hours to remove volatile matter, and further left in a desiccator for 15 minutes to measure the mass. The mass of the sample after removing the volatile matter was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration.

(3) Measurement of pigment-containing polymer particles and average particle size of polymer particles Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25 ° C., an angle of 90 ° between the incident light and the detector, and 100 times of integration, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measured concentration was 5 × 10 ^-3 % by mass (converted to solid content concentration).

(4) Measurement of viscosity of water-based ink Using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1 ° 34'x R24, rotation speed 50 rpm), viscosity at 32 ° C. Was measured.
(5) Static surface tension of water-based ink Using a surface tension meter (manufactured by Kyowa Interface Science Co., Ltd., trade name: CBVP-Z), a platinum plate is placed in a columnar polyethylene container containing 5 g of water-based ink (diameter 3. It was immersed in 6 cm × 1.2 cm in depth), and the static surface tension of the water-based ink was measured at 20 ° C.
(6) Measurement of pH of water-based ink A water-based system at 25 ° C. using a desktop pH meter "F-71" (manufactured by HORIBA, Ltd.) using a pH electrode "6337-10D" (manufactured by HORIBA, Ltd.). The pH of the ink was measured.

(7) Amount of water absorption of the recording medium when the contact time between the recording medium and pure water is 100 msec Using an automatic scanning liquid absorption meter (KM500win manufactured by Kumagai Riki Kogyo Co., Ltd.), conditions of 23 ° C. and 50% relative humidity. The transfer amount of pure water at a contact time of 100 ms was measured, and the water absorption amount was set to 100 ms. The measurement conditions are shown below.
"Spiral Method"
Contact Time: 0.010 to 1.0 (sec)
Pitch (mm): 7
Length Per Sampling (degree): 86.29
Start Radius (mm): 20 End Radius (mm): 60
Min Contact Time (ms): 10 Max Contact Time (ms): 1000
Sampling Pattern (1-50): 50
Number of Sampling Points (> 0): 19
"Square Head"
Slit Span (mm): 1 Slit Width (mm): 5

Production Example 1 (Synthesis of water-insoluble polymer)
16 parts of methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.), 44 parts of styrene (manufactured by Wako Pure Chemical Industries, Ltd.), styrene macromonomer "AS-6S" (manufactured by Toa Synthetic Co., Ltd., number average molecular weight 6,000, solid 30 parts (50%) and 25 parts of methoxypolyethylene glycol methacrylate "Blemmer PME-200" (Nichiyu Co., Ltd.) were mixed to prepare 115 parts of a monomer mixed solution.
In the reaction vessel, 18 parts of methyl ethyl ketone, 0.03 part of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixed solution are put and mixed, and nitrogen gas replacement is sufficiently performed. It was.
On the other hand, the remaining 90% (103.5 parts) of the monomer mixed solution, 0.27 parts of the chain transfer agent, 42 parts of methyl ethyl ketone and the polymerization initiator 2,2'-azobis (2,4-dimethylvaleronitrile) "V". -65 ”(manufactured by Wako Pure Chemical Industries, Ltd.) A mixed solution containing 3 parts was placed in a dropping funnel, and the temperature was raised to 75 ° C. while stirring the mixed solution in the reaction vessel under a nitrogen atmosphere. The mixed solution was added dropwise over 3 hours. After 2 hours have passed at 75 ° C. from the end of the dropwise addition, a solution prepared by dissolving 3 parts of the polymerization initiator in 5 parts of methyl ethyl ketone is added, and the mixture is further aged at 75 ° C. for 2 hours and 80 ° C. for 2 hours, and 50 parts of methyl ethyl ketone is further added. A solution of a water-insoluble polymer (weight average molecular weight: 50,000) was obtained. The solid content concentration of the water-insoluble polymer solution was 45% by mass.

Production Example 2 (Production of an aqueous dispersion of black pigment-containing polymer particles)
95.2 parts of the water-insoluble polymer solution obtained in Production Example 1 was dissolved in 53.9 parts of methyl ethyl ketone, and 15.0 parts of a 5N sodium hydroxide aqueous solution and 0.5 part of 25% ammonia water were contained therein as a neutralizing agent. , And 341.3 parts of ion-exchanged water were added, and C.I. I. 100 parts of Pigment Black 7 (P.B.7, manufactured by Cabot Corporation) was added to obtain a pigment mixture. The degree of neutralization was 78.8 mol%. The pigment mixture was mixed using a disper blade under the conditions of 7000 rpm and 20 ° C. for 1 hour. The obtained dispersion was subjected to 15-pass dispersion treatment at a pressure of 180 MPa using a microfluidizer "High Pressure Homogenizer M-140K" (manufactured by Microfluidics).
Methyl ethyl ketone is removed from the obtained dispersion of pigment-containing polymer particles at 60 ° C. under reduced pressure, some water is further removed, and the mixture is centrifuged, and the liquid layer portion is filtered with a filter "Minisalt Syringe Filter" (Zartorius). Co., Ltd., Pore diameter: 5 μm, Material: Cellulose acetate) was filtered to remove coarse particles, and an aqueous dispersion of pigment-containing polymer particles was obtained. The solid content concentration was 25% by mass. To 100 parts of the obtained aqueous dispersion of the pigment-containing polymer particles, 0.45 parts of Denacol EX321L (manufactured by Nagase ChemteX Corporation) and 15.23 parts of ion-exchanged water were added, and the mixture was stirred at 70 ° C. and 3 parts. The heat treatment was carried out for hours. After cooling to room temperature, the liquid layer is filtered through a filter "Mini Sartorius Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, and an aqueous dispersion (solid) of pigment-containing polymer particles. Particle concentration 22.0% by mass) was obtained. The average particle size of the pigment-containing polymer particles was 100 nm.

Production Examples 3 to 5 (Production of an aqueous dispersion of polymer particles containing cyan, magenta, and yellow pigments)
In Production Example 2, the black pigment is a cyan pigment (manufactured by DIC Corporation, P.B. 15: 3), a magenta pigment (manufactured by Fuji dye Co., Ltd., PR150), or a yellow pigment (Dainichiseika Kogyo Co., Ltd.). An aqueous dispersion of pigment-containing polymer particles (solid content concentration: 22% by mass) was obtained under the conditions shown in Table 1 instead of P.Y.74) manufactured by the company. The results are shown in Table 1.

Production Example 6 (Production of fixing aid polymer emulsion)
In a 1000 mL separable flask, 145 parts of methyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 50 parts of 2-ethylhexyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 5 parts of methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), Latemuru E118B (manufactured by Kao Co., Ltd., emulsifier, effective content 26%) 18.5 parts, ion-exchanged water 96 parts, potassium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.) were charged and stirred with a stirring blade (300 rpm). A monomer emulsion was obtained.
In the reaction vessel, 4.6 parts of Latemul E118B, 186 parts of ion-exchanged water, and 0.08 part of potassium persulfate were placed and replaced with nitrogen gas sufficiently. The temperature was raised to 80 ° C. while stirring (200 rpm) with a stirring blade in a nitrogen atmosphere, and the monomer emulsion charged in the dropping funnel was dropped over 3 hours to react. Ion-exchanged water was added to this reaction solution to obtain a fixing aid polymer emulsion having a solid content of 41.6% by weight. The average particle size of this polymer emulsion was 100 nm.

Manufacturing Example 7 (Manufacturing of black ink)
4626.75 g of an aqueous dispersion (solid content 22.0% by mass) of the black pigment-containing polymer particles obtained in Production Example 2, and a fixing aid polymer emulsion (solid content 41.6% by weight) obtained in Production Example 6. 438.87 g, diethylene glycol monoisobutyl ether 100.00 g, propylene glycol 2300.00 g, silicone-based activator (manufactured by Shin-Etsu Chemical Co., Ltd., KF-6011) 20.00 g, acetylene-based activator (manufactured by Nissin Chemical Industry Co., Ltd.) , Surfinol 440) 100.00 g and ion-exchanged water 2414.38 g were added and mixed. The obtained mixed solution was filtered through a filter "Mini Sartorius Syringe Filter" (manufactured by Sartorius, pore diameter: 5.0 μm, material: cellulose acetate) to obtain an aqueous ink. Table 2 shows various physical properties of the water-based ink.

Manufacturing Examples 8 to 10 (Manufacturing of cyan, magenta, and yellow ink)
In Production Example 7, the aqueous dispersion of the black pigment-containing polymer particles was changed to the aqueous dispersion of the cyan, magenta, and yellow pigment-containing polymer particles obtained in Production Examples 3 to 5, and under the conditions shown in Table 2. Cyan, magenta, and yellow water-based inks were obtained. The results are shown in Table 2. Further, the four color inks obtained in Production Examples 7 to 10 were used as the ink set 1. Each physical property is shown in Table 2.

Production Examples 11-14, 15-18, 19-22
Similar to Production Examples 7 to 10, the four color inks obtained by Production Examples 11 to 14 under the conditions shown in Table 2 are the ink set 2, the inks obtained by Production Examples 15 to 18 are the ink set 3, and Production Example. The inks obtained in 19 to 22 were designated as ink set 4. The results are shown in Table 2.

Examples 1-2, Comparative Example 1
The ink sets 1 to ² obtained in the production example were applied to the corona-treated PET (Taiko Polyester Film FE2001 manufactured by Futamura Chemical Co., Ltd., the water absorption of the recording medium at a contact time of 100 msec between the recording medium and pure water 0 g / m ² ). An image was formed by the following inkjet recording method using No. 4.
(Inkjet recording method)
A one-pass print evaluation device (manufactured by Kyocera Corporation, "KJ4B-HD06MHG-STDV", piezo type) equipped with an inkjet head (manufactured by Kyocera Corporation, "KJ4B-HD06MHG-STDV", manufactured by Tritech Co., Ltd.) in an environment with a temperature of 25 ± 1 ° C and a relative humidity of 30 ± 5%. ) Was filled with water-based ink. These inkjet heads are provided in the print evaluation device in the order of black ink, cyan ink, magenta ink, and yellow ink from the upstream side in the feeding direction of the recording medium. At this time, the distance between the respective inkjet heads filled with black ink, cyan ink, magenta ink, and yellow ink was set to 55 cm.
Head voltage 26V, frequency 10kHz, discharge liquid appropriate amount 3pl, head temperature 32 ° C, resolution 600dpi, number of flushing before discharge 200, negative pressure-4.0kPa are set, and the longitudinal direction and transport direction of the recording medium are the same. The recording medium was fixed to the print evaluation device.
The print evaluation device includes an inkjet head that ejects water-based ink onto the recording medium, and an underheater that heats the recording medium from a surface opposite to the surface of the recording medium facing the head. The distance between the underheater and the recording medium was set to 0.25 mm, the distance between the inkjet head and the recording medium was set to 1.0 mm, and the surface temperature of the underheater was set to 55 ° C. (the temperature of the recording medium was 50 ° C.). ..
An A4 size film heater (manufactured by Kawai Denki Seisakusho Co., Ltd.) was fixed to the recording medium carrier so that the recording medium could be heated. The film heater temperature was 20 ° C, 40 ° C, and 60 ° C. The transport speed of the recording medium was 25 m / min.
A print command is transferred to the print evaluation device, ink is ejected in the order of black ink, cyan ink, magenta ink, and yellow ink, and the three solid images of each color are orthogonally overlapped with each other. The pattern was printed. Then, it was dried in a warm air dryer at 60 ° C. for 5 minutes to obtain a printed matter.
The obtained printed matter was evaluated for color mixing, deformation of the base material due to heating, and solid uniformity by the following methods and criteria. The evaluation results are shown in Table 3.

(Color mixing evaluation method for printed matter)
In a portion where solid printed images of different colors of printed matter are orthogonal to each other and color mixing occurs, the width protruding from the orthogonal portion of the eroded portion with respect to the solid image of another color in which one color is orthogonal is measured. An average value was calculated from the measured values obtained for each combination of colors, the degree of color mixing was compared based on the average value, and evaluation was performed according to the following criteria.
A: The average value is less than 80 μm, and color mixing can hardly be confirmed.
B: The average value is 80 μm or more and less than 100 μm, and the color mixing is not conspicuous and there is no problem in actual use.
C: The average value is 100 μm or more and less than 200 μm, and some color mixing is confirmed, but there is no problem in actual use.
D: The average value is 200 μm or more, and clear color mixing is confirmed and it cannot be actually used.

(Evaluation criteria for deformation of printed matter due to heating)
A: No deformation of the printed matter is seen.
B: The printed matter is deformed.
(Evaluation criteria for solid print uniformity)
A: No unevenness in shading is seen in the solid print area.
B: Light and shade unevenness is observed in the area of the solid printed portion of less than 10%, but there is no problem in actual use.
C: There is unevenness in the area of 10% or more of the solid printed portion, and there is a problem in actual use.

Examples 3 and 4, Comparative Example 2
The same procedure as in Example 1 was carried out except that the ink set was changed to that shown in Table 3.
Example 5 and Comparative Example 3
The same procedure as in Example 1 was carried out except that the recording medium was changed from the corona-treated PET to the corona discharge-treated OPP (Taiko polypropylene film FOR-AQ manufactured by Futamura Chemical Co., Ltd.). In Comparative Example 3, the underheater temperature was further changed to 80 ° C.

In Table 3, from the comparison between Examples 1 and 2 and Comparative Example 1, the comparison between Examples 3 and 4 and Comparative Example 2, and the comparison between Example 5 and Comparative Example 3, the inkjet recording method of the example is described. It can be seen that, as compared with the inkjet recording method of the comparative example, there is less color mixing and deformation of the printed matter, and an image having excellent uniformity can be obtained.

Claims (9)

A method for recording on a low-liquidity recording medium using an inkjet recording device including an inkjet head that ejects water-based ink onto the recording medium.
The water-based ink contains a colorant (A), a fixing aid polymer (B-2), an organic solvent (C), and water.
The average particle size of the fixing aid polymer (B-2) particles in the water-based ink is 30 nm or more and 200 nm or less.
The inkjet recording device includes three or more types of water-based inks having different static surface tensions.
The recording medium is heated to 30-75 ° C.
An inkjet recording method in which water-based ink having a higher static surface tension is sequentially ejected onto the recording medium. The inkjet recording method according to claim 1, wherein the colorant (A) is contained in a water-based ink as water-insoluble polymer particles containing a pigment. The inkjet recording method according to claim 1 or 2, wherein the organic solvent (C) contains glycol ether (c-2). The inkjet recording method according to any one of claims 1 to 3, wherein the water-based ink further contains a surfactant (D). The inkjet recording method according to claim 4, wherein the surfactant (D) contains a silicone-based surfactant (d-1). The inkjet recording method according to any one of claims 1 to 5, wherein the low liquid absorption recording medium is a corona discharge-treated polyester film or a corona discharge-treated stretched polypropylene film. 7. Ink recording method. The inkjet recording method according to any one of claims 1 to 7, wherein the recording speed is 5 m / min or more and 75 m / min or less in terms of the transport speed of the recording medium. The inkjet recording method according to any one of claims 1 to 8, wherein recording is performed by a one-pass method.