JP2018127536A - Aqueous ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink excellent in storage stability and capable of providing a printed matter having excellent fixability and image quality even when a printing medium with low liquid absorptivity is used, while maintaining intermittent discharge stability during high speed printing, and an inkjet printing method using the aqueous ink.SOLUTION: There are provided [1] an aqueous ink containing a pigment (A), an organic solvent (B), a wax emulsion (C) and water, in which the organic solvent (B) contains alkanediol having 5 or less carbon atoms (b-1), the wax emulsion (C) contains an anionic wax emulsion (c-1), content of the anionic wax emulsion (c-1) in the wax emulsion (C) is 50 mass% or more, the wax emulsion (C) contains at least one kind of wax having the melting point of 110°C or more and an average particle diameter of the wax emulsion (C) is 400 nm or less, and [2] an inkjet printing method using the aqueous ink.SELECTED DRAWING: None

Description

  The present invention relates to a water-based ink and an inkjet printing method using the water-based ink.

The ink jet recording method is a recording method in which ink droplets are directly ejected from fine nozzles and attached to a printing medium to obtain a printed matter on which characters and images are recorded. This method is easy and inexpensive to make full-color, and has the advantage of non-contact with the substrate, so it is not limited to consumer printing for general consumers. In recent years, analog printing such as offset printing and gravure printing has been used. It has begun to be applied to commercial printing and industrial printing.
The advantage of developing inkjet printing in the commercial printing and industrial printing fields is that it does not require a printing plate unlike analog printing, and can be used for small-volume printing and on-demand printing such as variable printing.

In the commercial printing and industrial printing fields, high productivity is required compared to consumer printing, so high-speed printing is performed. In order to cope with this high-speed printing, a line head type print head has been developed. In the conventional serial head method, printing is performed by operating the head (nozzle) a plurality of times, whereas in the line head method, the head is fixed and only the print medium such as printing roll paper is scanned, so that high-speed printing is possible. Become. On the other hand, in the line head method, since the head passes through the print medium only once, if ink ejection failure occurs even with one nozzle, the image quality is immediately reduced, and therefore a higher level of ejection. Stability is required.
Further, in the commercial printing and industrial printing fields, the storage time until the ink is used may be long, and better storage stability is required.
For example, Patent Document 1 discloses that specific compounds such as pigments, polymer dispersants, and polypropylene glycols 0.01 to 0.01 in order to improve the intermittent discharge performance of ink when printing on sheet paper using a serial head method. An aqueous pigment ink containing 3% by weight, a water-soluble solvent, and water is disclosed.
Patent Document 2 discloses a pigment coated with a water-insoluble resin, water-insoluble having a glass transition temperature of 100 ° C. or higher in order to suppress ink blocking and blocking of the obtained image. An ink composition containing polymer particles, a solid wetting agent, a water-soluble organic solvent, wax particles having a melting point of 40 to 100 ° C., and water is disclosed.

Japanese Patent Laid-Open No. 10-53741 JP 2011-162692 A

In the ink jet recording system printing using water-based ink, the frequency of use is different for each nozzle, and the ink is less likely to be solidified because the drying of the ink proceeds at a nozzle with a low frequency of use.
Furthermore, in the field of commercial printing and industrial printing, in addition to printing on conventional liquid paper, high liquid-absorbing print media called copy paper, low liquid-absorbent coated paper such as offset coated paper, or polypropylene resin, There is a demand for printing on a printing medium such as a film of a non-absorbent resin such as a polyester resin. In these low liquid-absorbing or non-liquid-absorbing printing media, the ink is slowly absorbed or not absorbed, so that the pigment remains on the surface of the printing surface, and the fixability of the ink to the printing medium is insufficient. . For this reason, when the printing surface comes into contact with a transport roller or the like in the printing press, the pigment present on the surface of the printing surface is scraped off and transferred to the roller, so-called roller transfer occurs, and the printing area is reduced and the image quality of the printed matter deteriorates. There is a problem of doing.
In the water-based pigment ink of Patent Document 1 and the ink composition of Patent Document 2, the fixability of the ink to the print medium is not sufficient, and the suppression of the transfer of the pigment to the roller is insufficient. Improvement of the image quality of the printed matter obtained is desired. In the ink composition of Patent Document 2, a wax is used, and the melting point of the wax specifically used in Examples is 102 ° C. at the maximum.
The present invention is excellent in storage stability, and maintains high discharge stability (intermittent discharge stability) even in high-speed printing using an ink jet recording method, and excellent fixability and image quality even when using a low liquid-absorbing print medium. It is an object of the present invention to provide a water-based ink capable of obtaining a printed matter having the above-described properties and an ink jet printing method using the water-based ink.
In the present specification, “low liquid absorption” is a concept including low liquid absorption and non-liquid absorption, and the water absorption amount of the print medium when the contact time between the print medium and pure water is 100 ms. It means 0 g / m ² or more and 10 g / m ² or less.

The present inventors have excellent storage stability with a water-based ink containing a specific wax emulsion and a specific organic solvent, while maintaining high intermittent discharge stability even in high-speed printing using an ink jet recording method, while having low liquid absorption. It has been found that a printed matter having excellent fixability and image quality can be obtained even when a printing medium is used.
That is, the present invention provides the following [1] and [2].
[1] A water-based ink containing a pigment (A), an organic solvent (B), a wax emulsion (C) and water,
The organic solvent (B) contains an alkanediol (b-1) having 5 or less carbon atoms,
The wax emulsion (C) includes an anionic wax emulsion (c-1), and the content of the anionic wax emulsion (c-1) in the wax emulsion (C) is 50% by mass or more,
The wax emulsion (C) contains at least one wax having a melting point of 110 ° C. or higher,
A water-based ink in which the average particle size of the wax emulsion (C) is 400 nm or less.
[2] An inkjet printing method for discharging the aqueous ink according to [1] from a discharge nozzle of an inkjet print head onto a print medium,
The inkjet print head system is the line head system,
The printing speed is 70 m / min or more in terms of the conveyance speed of the printing medium,
An ink-jet printing method, wherein a water absorption amount of the print medium at a contact time of 100 msec between the print medium and pure water is 0 g / m ² or more and 10 g / m ² or less.

  According to the present invention, the printed matter has excellent storage stability and excellent fixability and image quality even when using a low liquid-absorbing print medium while maintaining high intermittent ejection stability even in high-speed printing using an inkjet recording method. Can be obtained, and an ink jet printing method using the water-based ink can be provided.

[Water-based ink]
The water-based ink of the present invention (hereinafter also simply referred to as “ink”) is a water-based ink containing a pigment (A), an organic solvent (B), a wax emulsion (C) and water, and the organic solvent (B) Containing an alkanediol (b-1) having 5 or less carbon atoms (hereinafter also simply referred to as “alkanediol (b-1)”), and the wax emulsion (C) is an anionic wax emulsion (c-1) (hereinafter referred to as “alkanediol (c-1)”). Simply referred to as “wax emulsion (c-1)”), the content of the wax emulsion (c-1) in the wax emulsion (C) is 50% by mass or more, and the wax emulsion (C) has a melting point of 110 The wax emulsion (C) has an average particle size of 400 nm or less.
“Aqueous” means that water accounts for the largest proportion in the medium in which the pigment is dispersed.
Since the water-based ink of the present invention has excellent storage stability and can obtain a good printed matter, it can be suitably used as a flexographic ink, a gravure printing ink, or an inkjet printing ink, and inkjet recording. Even in the high-speed printing of the system, the low liquid absorbency is maintained while maintaining the intermittent discharge stability of ink after a predetermined time has passed without discharging ink from the discharge nozzle (hereinafter also simply referred to as “intermittent discharge stability”). Since the printed matter obtained using the printing medium has excellent fixability and image quality, it is particularly preferable to use it as an ink for ink jet printing.

Using the water-based ink of the present invention, the storage stability is excellent, and the fixing property and the image quality are excellent even when using a low liquid-absorbing printing medium while maintaining high intermittent ejection stability even in high-speed printing of an ink jet recording method. There is an excellent effect that a printed matter having the above can be obtained. The reason is not clear, but it is thought as follows.
In the present invention, by containing a wax emulsion containing a wax having a melting point of 110 ° C. or higher and hardly melted, melting of wax particles in the vicinity of the discharge nozzle is suppressed. Further, the wax emulsion contains an anionic wax emulsion, the content of the anionic wax emulsion in the wax emulsion is 50% by mass or more, and the average particle size of the wax emulsion is in a specific range, Aggregation of the wax emulsion due to electrostatic repulsion is suppressed. As a result, it is considered that storage stability is improved and instability of intermittent ink ejection is suppressed. Furthermore, since the organic solvent to be used contains an alkanediol having 5 or less carbon atoms, it is considered that the wettability with respect to the printing medium is improved and excellent fixability and image quality can be exhibited.
On the other hand, when the wax emulsion does not contain a wax having a melting point of 110 ° C. or higher, or when the content of the anionic wax emulsion in the wax emulsion is less than 50% by mass, the discharge nozzle is used during intermittent printing. It is considered that the melting (or softening) and solidification of the wax are repeated in the vicinity to induce aggregation of the wax emulsion and adhesion to the nozzle member, thereby causing instability of intermittent discharge.

[Water-based ink]
The aqueous ink of the present invention contains a pigment (A), an organic solvent (B), a wax emulsion (C) and water.

<Pigment (A)>
The pigment (A) is more advantageous than the dye in terms of water resistance and weather resistance of the printed matter.
The pigment (A) may be either an inorganic pigment or an organic pigment. If necessary, they can be used in combination with extender pigments.
Specific examples of inorganic pigments include carbon black and metal oxides, and carbon black is particularly preferred for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Specific examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
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 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 types of products selected from Pigment Green are listed.
Examples of extender pigments include silica, calcium carbonate, and talc.

The pigment (A) is preferably contained in the ink as a self-dispersing pigment, a pigment dispersed with a polymer dispersant, or water-insoluble polymer particles containing the pigment.
The pigment (A) is a water-insoluble polymer particle containing the pigment (A) (hereinafter simply referred to as “pigment-containing”) from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink, and improving the fixability and print image quality. It is preferably contained as “polymer particles”.

[Water-insoluble polymer particles containing pigment (pigment-containing polymer particles)]
(Water-insoluble polymer)
The water-insoluble polymer has a function as a pigment dispersant that exhibits a pigment dispersing action and a function as a fixing agent for a print medium.
Here, “water-insoluble” means that when the polymer which has been dried at 105 ° C. for 2 hours and reaches a constant weight is dissolved in 100 g of water at 25 ° C., the dissolved amount is 10 g or less, The dissolved amount is preferably 5 g or less, more preferably 1 g or less. When the water-insoluble polymer is an anionic polymer, the amount dissolved is the amount dissolved when 100% of the anionic group of the polymer is neutralized with sodium hydroxide. When the water-insoluble polymer is a cationic polymer, the dissolution amount is the dissolution amount when the cationic group of the polymer is neutralized with hydrochloric acid 100%.
The existence form of the water-insoluble polymer in the ink includes a state in which it is adsorbed to the pigment, a state in which the pigment is contained (capsule), and a form in which the pigment is not adsorbed. From the viewpoint of the dispersion stability of the pigment, in the present invention, the form of the pigment-containing polymer particles is preferable, and the pigment-encapsulated state containing the pigment is more preferable.
Examples of water-insoluble polymers include polyesters, polyurethanes, and vinyl polymers. From the viewpoint of improving the storage stability of ink, vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds). Polymers are preferred.

  The vinyl polymer is preferably (a-1) an ionic monomer (hereinafter also referred to as “(a-1) component”) and (a-2) a hydrophobic monomer (hereinafter referred to as “(a-2) component”). Is a vinyl polymer obtained by copolymerization of a monomer mixture (hereinafter also referred to simply as “monomer mixture”). The vinyl polymer has a structural unit derived from the component (a-1) and a structural unit derived from the component (a-2). Among them, (a-3) a structural unit derived from a macromonomer (hereinafter also referred to as “(a-3) component”) or (a-4) a nonionic monomer (hereinafter referred to as “(a-4) component”). More preferred are vinyl polymers having structural units derived from.

[(A-1) Ionic monomer]
(A-1) The ionic monomer is preferably used as a monomer component of the water-insoluble polymer from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink. Examples of the ionic monomer include an anionic monomer and a cationic monomer, and an anionic monomer is preferable. Note that the ionic monomer includes a monomer that becomes an ion under acidic or alkaline conditions, even if it is a neutral non-ionic monomer such as an acid or an amine.
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, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Among the anionic monomers, a carboxylic acid monomer is preferable, acrylic acid and methacrylic acid are more preferable, and methacrylic acid is further preferable from the viewpoint of improving dispersion stability of the pigment-containing polymer particles in the ink.
Examples of the cationic monomer include N, N-dimethylaminoethyl methacrylate and N, N-dimethylaminoethylacrylamide.

[(A-2) Hydrophobic monomer]
(A-2) The hydrophobic monomer is preferably used as a monomer component of the water-insoluble polymer from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink. Examples of the hydrophobic monomer include alkyl (meth) acrylic acid esters and aromatic group-containing monomers.
The alkyl (meth) acrylic acid ester preferably has an alkyl group having 1 to 22 carbon atoms, and more preferably has an alkyl group having 6 to 18 carbon atoms. For example, methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, Examples include 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) stearyl (meth) acrylate, and the like.
In addition, “(iso or tertiary)” and “(iso)” mean both cases where these prefixes exist and when they do not exist, and indicate normal when these prefixes do not exist. “(Meth) acrylic acid” means one or more selected from acrylic acid and methacrylic acid, and “(meth) acrylic ester” means one selected from acrylic acid ester and methacrylic acid ester. That means the above. Therefore, “(meth) acrylate” means one or more selected from acrylate and methacrylate. “(Meta)” in the following is also synonymous.

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 hetero atom, is preferable, and a styrenic monomer, an aromatic group-containing (meth) Acrylic acid esters are more preferred. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
As the styrenic monomer, styrene, 2-methylstyrene, and divinylbenzene are preferable, and styrene is more preferable.
Moreover, as an aromatic group containing (meth) acrylic acid ester, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc. are preferable, and benzyl (meth) acrylate is more preferable.
(A-2) The hydrophobic monomer is preferably an aromatic group-containing monomer, more preferably at least one selected from a styrene monomer and an aromatic group-containing (meth) acrylic ester, and more preferably styrene. Monomer, and more preferably styrene.
(A-2) Two or more of the above monomers may be used as the hydrophobic monomer, or a styrene monomer and an aromatic group-containing (meth) acrylic acid ester may be used in combination.

[(A-3) Macromonomer]
(A-3) The macromonomer is a compound having a polymerizable functional group at one end and a number average molecular weight of 500 or more and 100,000 or less, and from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink. It is preferably used as a monomer component of an insoluble polymer. The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group.
(A-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 using polystyrene as a standard substance by gel permeation chromatography using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent.
(A-3) As the macromonomer, from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink, an aromatic group-containing macromonomer and a silicone-based macromonomer are preferable, and an aromatic group-containing macromonomer is more preferable. .
Examples of the aromatic group-containing monomer constituting the aromatic group-containing macromonomer include the aromatic group-containing monomers described in the above (a-2) hydrophobic monomer, styrene and benzyl (meth) acrylate are preferred, and styrene is preferred. More preferred.
Specific examples of the styrenic macromonomer include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toagosei Co., Ltd.), and the like.
Examples of the silicone macromonomer include organopolysiloxane having a polymerizable functional group at one end.

[(A-4) Nonionic monomer]
In the water-insoluble polymer, from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink, (a-4) a nonionic monomer (hereinafter also referred to as “component (a-4)”) is used as a monomer component. It is preferable to use it.
As component (a-4), hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; polypropylene glycol (n = 2 to 30, n is an average of alkylene oxide) The number of moles added is the same. The same applies hereinafter. Poly (alkylene glycol) mono (meth) acrylates such as mono (meth) acrylate and polyethylene glycol (n = 2 to 30) mono (meth) acrylate; methoxypolyethylene glycol (n = 1 to 30) Alkoxypolyalkylene glycol (meth) acrylates such as (meth) acrylate; Phenoxy (ethylene glycol-propylene glycol copolymer) (n = 1 to 30, ethylene glycol: n = 1 to 29 therein) (meth) acrylate, etc. Cited . Among these, polyalkylene glycol mono (meth) acrylate is preferable, and polypropylene glycol (n = 2 to 30) mono (meth) acrylate is more preferable.

As a commercial item of (a-4) component, NK ester M-20G, 40G, 90G, 230G, etc. (above, trade name of Shin-Nakamura Chemical Co., Ltd.), Bremer PE-90, 200, 350 etc., PME-100, 200, 400 etc., Blemmer PP-500, 800, 1000 etc., AP-150, 400, 550 etc., 50 PEP-300, 50 POEP-800B, 43 PAPE-600B etc. The above is a product name of NOF Corporation.
The components (a-1) to (a-4) can be used alone or in admixture of two or more.

(Content of each component or structural unit in the monomer mixture or polymer)
Content of the above-mentioned components (a-1) to (a-4) in the monomer mixture at the time of producing the water-insoluble polymer or structural units derived from the components (a-1) to (a-4) in the water-insoluble polymer The content is as follows from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink.
The content of the component (a-1) is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, still more preferably 10% by mass or more, and preferably 30%. It is not more than mass%, more preferably not more than 25 mass%, still more preferably not more than 20 mass%.
The content of the component (a-2) is preferably 25% by mass or more, more preferably 30% by mass or more, still more preferably 35% by mass or more, still more preferably 40% by mass or more, and preferably 60% by mass. % Or less, more preferably 55% by mass or less, and still more preferably 50% by mass or less.
The content of the component (a-3) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass. % Or less, more preferably 20% by mass or less.
The content of the component (a-4) is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, still more preferably 25% by mass or more, and preferably 40%. It is not more than mass%, more preferably not more than 35 mass%, still more preferably not more than 30 mass%.
The mass ratio of the component (a-1) to the component (a-2) [(a-1) component / (a-2) component] is preferably 0.05 or more, more preferably 0.15 or more, and still more preferably. Is 0.25 or more, and preferably 1.2 or less, more preferably 0.80 or less, still more preferably 0.50 or less, and still more preferably 0.40 or less.
The mass ratio of the component (a-1) to the total amount of the component (a-2) and the component (a-3) [(a-1) component / [(a-2) component + (a-3) component] ] Is preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.10 or more, still more preferably 0.20 or more, and preferably 1 or less, more preferably 0. It is 60 or less, more preferably 0.40 or less, and still more preferably 0.30 or less.

(Production of water-insoluble polymer)
The water-insoluble polymer is produced by copolymerizing a monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
Although there is no restriction | limiting in the solvent used by the solution polymerization method, Polar organic solvents, such as C1-C3 aliphatic alcohol, ketones, ethers, and esters, are preferable, specifically, methanol, ethanol, acetone, and methyl ethyl ketone. And methyl ethyl ketone is preferred.
In the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. As the polymerization initiator, an azo compound is preferable, and 2,2′-azobis (2,4-dimethylvaleronitrile) is more preferable. . As the polymerization chain transfer agent, mercaptans are preferable, and 2-mercaptoethanol is more preferable.

Although preferable polymerization conditions vary depending on the type of polymerization initiator and the like, the polymerization temperature is preferably 50 ° C. or higher and 90 ° C. or lower, and the polymerization time is preferably 1 hour or longer and 20 hours or shorter. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. In addition, unreacted monomers and the like can be removed from the obtained polymer by reprecipitation, membrane separation, chromatographic methods, extraction methods and the like.
From the viewpoint of improving the productivity of the aqueous dispersion of pigment-containing polymer particles to be described later, the water-insoluble polymer is used as an organic solvent used in Step I to be described later without removing the solvent used in the polymerization reaction. For use, it is preferably used as it is as a water-insoluble polymer solution.
From the viewpoint of improving the productivity of the aqueous dispersion of pigment-containing polymer particles, the solid content concentration of the water-insoluble polymer solution is preferably 30% by mass or more, more preferably 40% by mass or more, and still more preferably 50% by mass or more. Yes, and preferably 70% by mass or less, more preferably 65% by mass or less.
The weight average molecular weight of the water-insoluble polymer used in the present invention further improves the dispersion stability of the pigment-containing polymer particles in the ink, and further improves the storage stability and intermittent ejection stability of the ink. From the viewpoint of improving the image quality, it is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 20,000 or more, still more preferably 30,000 or more, and preferably 500,000 or less. More preferably, it is 400,000 or less, More preferably, it is 300,000 or less, More preferably, it is 200,000 or less, More preferably, it is 100,000 or less.
In addition, the measurement of a weight average molecular weight can be performed by the method as described in an Example.

[Production of pigment-containing polymer particles]
The aqueous ink of the present invention preferably contains water-insoluble polymer particles containing the pigment (A).
Water-insoluble polymer particles (pigment-containing polymer particles) containing the pigment (A) can be efficiently produced by a method having the following step I and step II as an aqueous dispersion.
Step I: A step of dispersing a mixture containing a water-insoluble polymer, an organic solvent, a pigment (A), and water (hereinafter also referred to as “pigment mixture”) to obtain a dispersion of pigment-containing polymer particles Step II: 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”).

(Process I)
In Step I, first, the water-insoluble polymer is dissolved in an organic solvent, and then the pigment (A), water, and, if necessary, a neutralizing agent and a surfactant are added to the obtained organic solvent solution and mixed. A method of obtaining an oil-in-water type dispersion is preferred. Although there is no restriction | limiting in the order added to the organic solvent solution of a water-insoluble polymer, It is preferable to add in order of water, a neutralizing agent, and a pigment (A).
Although there is no restriction | limiting in the organic solvent in which a water-insoluble polymer is dissolved, C1-C3 aliphatic alcohol, ketones, ethers, esters, etc. are preferable, the wettability to a pigment (A), water-insoluble polymer From the viewpoint of improving the solubility and the adsorptivity of the water-insoluble polymer to the pigment (A), ketones having 4 to 8 carbon atoms are more preferred, methyl ethyl ketone and methyl isobutyl ketone are more preferred, and methyl ethyl ketone is even more preferred.
When a water-insoluble polymer is synthesized by a solution polymerization method, the solvent used in the polymerization may be used as it is.

(Neutralization)
When the water-insoluble polymer is an anionic polymer, an anionic group in the water-insoluble polymer may be neutralized using a neutralizing agent. When using a neutralizing agent, it is preferable to neutralize so that pH may be 7 or more and 11 or less.
Examples of the neutralizing agent include alkali metal hydroxides, ammonia, and organic amines. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide, and sodium hydroxide is preferable. Examples of the organic amine include trimethylamine, ethylamine, diethylamine, triethylamine, and triethanolamine.
From the viewpoint of further improving the intermittent ejection stability and storage stability of the ink, the neutralizing agent is preferably an alkali metal hydroxide or ammonia, and more preferably used in combination with sodium hydroxide and ammonia. Further, the water-insoluble polymer may be neutralized in advance.
The neutralizing agent is preferably used as an aqueous neutralizing agent solution from the viewpoint of sufficiently and uniformly promoting neutralization. From the above viewpoint, the concentration of the neutralizing agent aqueous solution is preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass. % Or less.
The degree of neutralization of the anionic group of the water-insoluble polymer is preferably 30 mol% or more, more preferably 40, from the viewpoint of improving the dispersion stability and storage stability of the pigment-containing polymer particles in the pigment aqueous dispersion and ink. It is at least mol%, more preferably at least 50 mol%, and preferably at most 300 mol%, more preferably at most 200 mol%, still more preferably at most 150 mol%.
Here, the degree of neutralization is obtained by dividing the molar equivalent of the neutralizing agent by the molar amount of the anionic group of the water-insoluble polymer.

(Content of each component in the pigment mixture)
The content of the pigment (A) in Step I in the pigment mixture further improves the dispersion stability of the pigment water dispersion, and further improves the storage stability and intermittent ejection stability of the ink, and fixes and print image quality. From the viewpoint of improving, preferably 10% by mass or more, more preferably 12% by mass or more, still more preferably 14% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably. Is 20% by mass or less.
The content of the water-insoluble polymer in the pigment mixture is a viewpoint that improves the dispersion stability of the pigment water dispersion, and further improves the storage stability and intermittent ejection stability of the ink, and the viewpoint that the fixability and print image quality are improved. Therefore, it is preferably 2% by mass or more, more preferably 4% by mass or more, further preferably 5% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, and further preferably 10% by mass. It is as follows.
The content of the organic solvent in the pigment mixture is preferably 10% by mass or more, more preferably 12% by mass or more, from the viewpoint of improving the wettability to the pigment (A) and the adsorptivity of the water-insoluble polymer to the pigment. More preferably, it is 15% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and still more preferably 25% by mass or less.
The content of water in the pigment mixture is preferably 40% by mass or more, more preferably 45% by mass or more, and still more preferably from the viewpoint of improving the dispersion stability of the pigment water dispersion and improving the productivity. It is 50% by mass or more, and preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less.

  The mass ratio of the pigment (A) to the water-insoluble polymer in the pigment mixture [pigment (A) / water-insoluble polymer] is the viewpoint of improving the dispersion stability of the pigment water dispersion, and the storage stability and intermittent ejection stability of the ink. From the viewpoint of further improving the fixability and improving the fixability and the print image quality, it is preferably 30/70 or more, more preferably 40/60 or more, still more preferably 50/50 or more, and even more preferably 60/40 or more. And, it is preferably 90/10 or less, more preferably 80/20 or less, and still more preferably 75/25 or less.

(Dispersion treatment of pigment mixture)
In step I, the pigment mixture is subjected to a dispersion treatment to obtain a dispersion of pigment-containing polymer particles. There is no particular limitation on the dispersion method for obtaining the dispersion. Although the average particle size of the pigment particles can be atomized only by the main dispersion until the desired particle size is reached, preferably the pigment mixture is pre-dispersed and further subjected to shear stress to perform the main dispersion. It is preferable to control the average particle size of the particles so as to have a desired particle size.
The temperature in the preliminary dispersion in step I is preferably 0 ° C. or higher, and preferably 40 ° C. or lower, more preferably 30 ° C. or lower, and further preferably 25 ° C. or lower. The dispersion time is preferably 0.5 hours. More preferably, it is 0.8 hours or longer, and preferably 30 hours or shorter, more preferably 10 hours or shorter, still more preferably 5 hours or shorter.
When the pigment mixture is predispersed, commonly used mixing and stirring devices such as anchor blades and disper blades can be used, and among them, a high-speed stirring and mixing device is preferable.

Examples of means for imparting the shear stress of this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidizer (manufactured by Microfluidic), a media-type disperser such as a paint shaker and a bead mill. Examples of commercially available media dispersers include Ultra Apex Mill (manufactured by Kotobuki Industries Co., Ltd.), Picomill (manufactured by Asada Tekko Co., Ltd.), and the like. A plurality of these devices can be combined. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When this 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.
The processing pressure is preferably 60 MPa or more, more preferably 100 MPa or more, still more preferably 130 MPa or more, and preferably 200 MPa or less, more preferably 180 MPa or less, from the viewpoints of productivity and economy.
The number of passes is preferably 3 or more, more preferably 10 or more, and preferably 30 or less, more preferably 25 or less.

(Process II)
In Step II, an aqueous dispersion of pigment-containing polymer particles (pigment water dispersion) can be obtained by removing the organic solvent from the dispersion obtained in Step I by a known method. The organic solvent in the obtained pigment aqueous dispersion is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
If necessary, the dispersion can be heated and stirred before the organic solvent is distilled off.
The obtained pigment aqueous dispersion is obtained by dispersing solid water-insoluble polymer particles containing the pigment (A) in a medium containing water as a main medium. Here, the form of the pigment-containing polymer particles is not particularly limited, as long as the particles are formed of at least the pigment (A) and the water-insoluble polymer. For example, the particle form in which the pigment (A) is encapsulated in the water-insoluble polymer, the particle form in which the pigment (A) is uniformly dispersed in the water-insoluble polymer, and the pigment (A) is exposed on the particle surface of the water-insoluble polymer. Particle morphology and the like are included, and mixtures thereof are also included.

The non-volatile component concentration (solid content concentration) of the obtained pigment aqueous dispersion is preferably 10% by mass or more, more preferably from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating ink preparation. Is 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.
The solid content concentration of the pigment aqueous dispersion is measured by the method described in the examples.
The average particle diameter of the pigment-containing polymer particles in the pigment aqueous dispersion is preferably 40 nm or more, more preferably 60 nm or more, and still more preferably 75 nm, from the viewpoint of reducing coarse particles and further improving the intermittent ejection stability of the ink. More preferably, the thickness is 90 nm or more, and preferably 150 nm or less, more preferably 120 nm or less, still more preferably 110 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in the examples.
The pigment-containing polymer particles in the ink are preferably free from swelling and shrinking of the particles and aggregation between the particles. The average particle diameter of the pigment-containing polymer particles in the ink is the average in the pigment aqueous dispersion. The preferable average particle diameter is the same as the particle diameter, and the preferable average particle diameter is the same as the preferable average particle diameter in the pigment aqueous dispersion. The average particle diameter of the pigment-containing polymer particles in the ink is also measured by the same method as the average particle diameter of the pigment-containing polymer particles in the pigment aqueous dispersion described in the Examples.

<Organic solvent (B)>
The organic solvent (B) contains alkanediol (b-1) having 5 or less carbon atoms from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink, and improving the fixability and the print image quality.
The carbon number of the alkanediol (b-1) is preferably 1 or more, more preferably 2 or more, and is preferably 4 or less, more preferably 3 or less, and even more preferably 3.
Specific examples of the alkanediol (b-1) include ethylene glycol (boiling point 197 ° C.), propylene glycol (boiling point 188 ° C.), 1,3-propanediol (boiling point 210 ° C.), 1,2-butanediol (boiling point). 194 ° C), 1,3-butanediol (boiling point 208 ° C), 1,4-butanediol (boiling point 230 ° C), 3-methyl-1,3-butanediol (boiling point 203 ° C), 1,5-pentanediol (Boiling point 242 ° C.). Among these, Preferably it is 1 or more types chosen from propylene glycol, 1, 2- butanediol, and 1, 5- pentanediol, More preferably, it is propylene glycol.
The boiling point of the organic solvent (B) is preferably 150 ° C. or higher, more preferably 160 ° C. or higher, and further preferably, from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink and improving the fixability and print image quality. Is 180 ° C. or higher, and from the same viewpoint as described above, preferably 250 ° C. or lower, more preferably 246 ° C. or lower, still more preferably 215 ° C. or lower, still more preferably 210 ° C. or lower, still more preferably 200 ° C. It is as follows.
In addition, when using 2 or more types of organic solvents as an organic solvent (B), the boiling point of an organic solvent (B) is a weighted average value weighted with content (mass%) of the several organic solvent from which a boiling point differs. .
The content of the alkanediol (b-1) in the organic solvent (B) is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and still more preferably substantially 100%. % By mass.

  The organic solvent (B) may contain an organic solvent other than the alkanediol (b-1). Examples thereof include polyhydric alcohols other than alkanediol (b-1), polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, and the like. Among these, at least one selected from polyhydric alcohols other than alkanediol (b-1), polyhydric alcohol alkyl ethers and nitrogen-containing heterocyclic compounds is preferable, and polyhydric alcohols other than alkanediol (b-1) and One or more selected from nitrogen-containing heterocyclic compounds are more preferable.

Examples of polyhydric alcohols other than alkanediol (b-1) include diethylene glycol (boiling point 244 ° C.), polyethylene glycol, dipropylene glycol (boiling point 232 ° C.), 1,6-hexanediol (boiling point 250 ° C.), 2- Methyl-2,4-pentanediol (boiling point 196 ° C.), 1,2,6-hexanetriol (boiling point 178 ° C.), 1,2,4-butanetriol (boiling point 190 ° C.), 1,2,3-butanetriol (Boiling point 175 ° C.), petriol (boiling point 216 ° C.) and the like.
In addition, polyhydric alcohols having a boiling point exceeding 250 ° C., such as triethylene glycol (boiling point 285 ° C.), tripropylene glycol (boiling point 273 ° C.), glycerin (boiling point 290 ° C.), Can be used in combination with a polyhydric alcohol having a boiling point of less than 230 ° C.

Examples of the polyhydric alcohol alkyl ether include ethylene glycol monoethyl ether (boiling point 135 ° C.), ethylene glycol monobutyl ether (boiling point 171 ° C.), diethylene glycol monomethyl ether (boiling point 194 ° C.), diethylene glycol monoethyl ether (boiling point 202 ° C.), Diethylene glycol monoisopropyl ether (boiling point 207 ° C), diethylene glycol monobutyl ether (boiling point 230 ° C), triethylene glycol monomethyl ether (boiling point 122 ° C), triethylene glycol monoisobutyl ether (boiling point 160 ° C), tetraethylene glycol monomethyl ether (boiling point 158) ° C), propylene glycol monoethyl ether (boiling point 133 ° C), dipropylene glycol monobutyl ether (boiling point) 227 ° C.), dipropylene glycol monomethyl ether (boiling point 90 ° C.), tripropylene glycol monomethyl ether (boiling point 100 ° C.), tripropylene glycol monobutyl ether. Among these, diethylene glycol monoisopropyl ether and dipropylene glycol monomethyl ether are preferable.
Examples of the nitrogen-containing heterocyclic compound include N-methyl-2-pyrrolidone (boiling point 202 ° C.), 2-pyrrolidone (boiling point 245 ° C.), 1,3-dimethylimidazolidinone (boiling point 220 ° C.), ε-caprolactam ( Boiling point 136 ° C.). Among these, N-methyl-2-pyrrolidone and 2-pyrrolidone are preferable.

<Wax emulsion (C)>
The wax emulsion (C) includes an anionic wax emulsion (c-1) from the viewpoint of improving the storage stability and intermittent ejection stability of the ink, and improving the fixing property and the printing image quality, and the wax emulsion (C). The content of the anionic wax emulsion (c-1) is 50% by mass or more, contains at least one wax having a melting point of 110 ° C. or more, and the average particle size of the wax emulsion (C) is 400 nm or less. .
The wax emulsion (C) only needs to contain at least one wax having a melting point of 110 ° C. or higher, and may contain a wax having a melting point of less than 110 ° C.
The content of the wax having a melting point of 110 ° C. or higher is preferable in the total amount of wax contained in the wax emulsion (C) from the viewpoint of improving the storage stability and intermittent discharge stability of the ink, and improving the fixability and the print image quality. Is 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, and still more preferably 100% by mass.
The melting point of the wax contained in the wax emulsion (C) is preferably 115 ° C or higher, more preferably 120 ° C or lower, and preferably 150 ° C or lower, more preferably 145 ° C or lower, still more preferably 140 ° C or lower. is there.
The melting point of the wax can be measured by the method described in the examples.

Examples of the wax emulsion (C) include wax emulsions containing polyolefin wax, paraffin wax, sazol wax and the like.
The polyolefin wax is a polymer or copolymer having an olefin monomer as a main component. The paraffin wax is preferably a petroleum wax made of a mixture of chain saturated hydrocarbons having 20 to 30 carbon atoms. Sazol wax is a synthetic wax composed of substantially linear saturated hydrocarbons produced from carbon monoxide and hydrogen as raw materials by the Fischer-Tropsch process.
Among these wax emulsions, a wax emulsion containing at least one selected from polyolefin wax and paraffin wax from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink, and improving the fixing property and the print image quality. And a wax emulsion containing a polyolefin wax is more preferable.

Examples of the olefin monomer used for the polyolefin wax include chain olefins having 2 to 12 carbon atoms such as ethylene, propylene, butene, hexene, methylbutene, methylpentene, and methylhexene, and cyclic olefins such as norbornene. Among these, those containing a chain olefin as a main component are preferred, and those containing ethylene, propylene or butene as a main component are more preferred. Specific examples include polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, propylene-butene copolymer, ethylene-propylene-butene copolymer, and ethylene-vinyl acetate copolymer. Among these, a polyolefin-based wax (polyethylene wax) containing ethylene as a main component is more preferable. Here, the main component preferably accounts for 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, and still more preferably 80% by mass or more with respect to the total components constituting the wax. Say.
The oxidized polyolefin wax is obtained by oxidizing a polyolefin wax by a known method and can be easily emulsified in an aqueous solvent, so that it is also preferably used as a polyolefin wax. The oxidized polyolefin wax can be obtained by introducing an oxygen atom or the like into the molecule while adjusting the high molecular weight polyolefin resin to a desired molecular weight by thermal decomposition or chemical decomposition. In addition, modified polyolefin waxes such as glycol-modified polyethylene wax can also be used.
In the present invention, oxidized polyolefin wax and modified polyolefin wax are also included in the polyolefin wax.
The wax emulsion containing the above wax can be used alone or in combination of two or more.

  The total content of one or more selected from polyolefin wax, paraffin wax, and sazol wax is preferably 65 parts by mass or more, more preferably 80 parts by mass or more, and still more preferably with respect to 100 parts by mass of the total amount of wax. 90 parts by mass or more, more preferably 95 parts by mass or more, and still more preferably 100 parts by mass.

The wax emulsion (C) includes an anionic wax emulsion (c-1), and the content of the wax emulsion (c-1) is 50% by mass or more in the wax emulsion (C). Thereby, aggregation of the wax emulsion due to electrostatic repulsion is suppressed, and the storage stability and intermittent ejection stability of the ink are improved.
The content of the wax emulsion (c-1) is preferably 60% by mass or more, more preferably 70% by mass or more in the wax emulsion (C) from the viewpoint of improving the storage stability and intermittent ejection stability of the ink. More preferably, it is 80 mass% or more, More preferably, it is 90 mass% or more, More preferably, it is 100 mass%.

The method for obtaining the anionic wax emulsion (c-1) is not particularly limited. For example, a method of emulsifying by mixing a polyolefin wax, other waxes used as necessary, and a known anionic surfactant, and the like can be mentioned. Examples of anionic surfactants include sulfate and phosphate ester salts based on ethylene oxide adducts of higher alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol and oleyl alcohol, and benzenesulfone alkylated with dodecyl groups. Acid salts.
As another method, an anionic group such as a carboxy group contained in the wax may be used, and a self-dispersing wax emulsion may be obtained by adding an alkali metal hydroxide, ammonia or the like as a neutralizing agent.
Among these, an anionic wax emulsion obtained by emulsifying a wax with an anionic surfactant is preferable from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink and improving the fixing property and the print image quality.
Commercially available products of the anionic wax emulsion (c-1) include BYQUA's AQUACER 507, 537, 1547, and 526, San Nopco's PEM-17, Mitsui Chemicals' Chemipearl W900, and W4005. And polyethylene wax emulsions.

The wax emulsion (C) may contain a wax emulsion other than the wax emulsion (c-1). Other wax emulsions include nonionic wax emulsions.
Examples of the wax emulsion other than the wax emulsion (c-1) include a method of emulsifying a mixture of a polyolefin-based wax, other wax used as necessary, and a nonionic surfactant. Nonionic surfactants include ethylene oxide adducts of higher alcohols such as lauryl alcohol, cetyl alcohol, oleyl alcohol, stearyl alcohol, and ethylene oxide adducts of phenol alkylated with octyl, nonyl, dodecyl, etc. .
Other commercially available wax emulsions other than the wax emulsion (c-1) include BYQUA's AQUACER 513, 515, 526, 531, 533, 539, 552, and cellosol manufactured by Chukyo Yushi Co., Ltd. 428, H620, 686, 524, Trasol CN, Polylon L-787, L-788, and the like.

The average particle size (average dispersed particle size) of the wax emulsion (C) in the ink further improves the dispersion stability of the wax emulsion, the storage stability of the ink, and the intermittent ejection stability, and improves the fixability and print image quality. In view of the above, it is 400 nm or less, preferably 300 nm or less, more preferably 200 nm or less, further 100 nm or less, still more preferably 80 nm or less, still more preferably 60 nm or less, and preferably 10 nm or more, more preferably It is 30 nm or more, more preferably 40 nm or more.
The average particle size (average dispersed particle size) of the wax emulsion (C) can be measured by a dynamic light scattering method. For example, using a Microtrac particle size analyzer UPA manufactured by Nikkiso Co., Ltd. according to the method described in the examples. Can be measured.
When two or more kinds of wax emulsions are used as the wax emulsion (C), the average particle diameter of the wax emulsion (C) is a weighted average value weighted by the content (mass%) of a plurality of wax emulsions. is there.

The pH of the wax emulsion (C) is preferable from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink, compatibility with other components in the ink, and suppressing corrosion of the metal in the inkjet nozzle and the like. Is 7 or more, more preferably 8 or more, still more preferably 9 or more, and is preferably 12 or less, more preferably 11 or less, and even more preferably 10 or less.
In addition, pH can be measured by the method as described in an Example.

<Surfactant (D)>
The aqueous ink of the present invention preferably contains a surfactant (D) from the viewpoint of suppressing an increase in ink viscosity, further improving intermittent ejection stability, and improving fixability and print image quality.
As the surfactant (D), from the above viewpoint, a nonionic surfactant is preferable, and an acetylene glycol surfactant is more preferable.
As the acetylene glycol surfactant, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 5-dimethyl-3-hexyne-2,5-diol, 2,5,8,11-tetramethyl-6-dodecin-5,8-diol, 3,5-dimethyl-1-hexyn-3-ol, and One or more selected from these EO adducts, more preferably 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3, One or more selected from 6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and EO adducts thereof, more preferably 2,4,7,9-tetramethyl- 5-decyne-4,7-dio And at least one member selected from the EO adducts.

2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 2,5-dimethyl-3-hexyne-2, 5-Diol can be synthesized by reacting acetylene with a ketone or aldehyde corresponding to the target acetylene glycol. For example, Takehiko Fujimoto, the revised edition “Introduction to New Surfactant” (Sanyo Kasei) Kogyo Co., Ltd., 1992), pages 94 to 107, and the like.
As the acetylene glycol surfactant, a compound having an average added mole number of ethylene oxide (hereinafter referred to as EO) of acetylene glycol of preferably 5 or more and 35 or less is preferable from the viewpoint of suppressing an increase in ink viscosity.
The EO average addition mole number of the acetylene glycol surfactant is more preferably 7 or more, still more preferably 8 or more, still more preferably 9 or more, still more preferably 9.5 or more, and more preferably 30. Hereinafter, more preferably 25 or less.
The ethylene oxide adduct of acetylene glycol can be obtained by subjecting the acetylene glycol obtained by the above method to an addition reaction so that ethylene oxide has a desired number of additions.
Examples of commercially available surfactants (D), particularly acetylene glycol surfactants, include “Surfinol 465 (EO average added mole number: 10, HLB) manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals. : 13) "," Surfinol 485 (EO average added mole number: 30, HLB: 17) "," Acetyleneol E81 (EO average added mole number: 8.1, HLB: 12) "manufactured by Kawaken Fine Chemical Co., Ltd. , “Acetylenol E100 (EO average addition mole number: 10, HLB: 13)”, “acetylene E200 (EO average addition mole number: 20, HLB: 16)” and the like.

(Pigment (A) content)
The content of the pigment (A) in the ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and further preferably 2.5% by mass or more, from the viewpoint of improving the printing density of the ink. It is. Further, from the viewpoint of lowering the ink viscosity at the time of solvent volatilization, further improving the intermittent ejection stability, and improving the fixability and print image quality, it is preferably 15.0% by mass or less, more preferably 10.0% by mass or less. More preferably, it is 7.0 mass% or less, More preferably, it is 5.0 mass% or less.
(Total content of pigment (A) and water-insoluble polymer)
The total content of the pigment (A) and the water-insoluble polymer in the ink is preferably 2.0% by mass or more, more preferably 2.5% by mass or more, still more preferably 3.0% by mass or more, and still more preferably. Is 3.5% by mass or more, and preferably 17.0% by mass or less, more preferably 12.0% by mass or less, still more preferably 10.0% by mass or less, and still more preferably 8.0% by mass. Hereinafter, it is more preferably 6.0% by mass or less.
The mass ratio [pigment (A) / water-insoluble polymer] of the pigment (A) to the water-insoluble polymer in the ink further improves the storage stability and intermittent ejection stability of the ink, and improves the fixability and print image quality. Therefore, it is preferably 30/70 or more, more preferably 40/60 or more, still more preferably 50/50 or more, still more preferably 60/40 or more, and preferably 90/10 or less, more preferably 80 / 20 or less, more preferably 75/25 or less.

(Content of organic solvent (B))
The content of the organic solvent (B) in the ink is preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more, from the viewpoint of further improving the intermittent ejection stability of the ink. More preferably, it is 25% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less, and still more preferably 35% by mass or less.
The content of alkanediol (b-1) in the ink is preferably 8% by mass or more, more preferably 12% by mass or more, and still more preferably 16% by mass or more from the viewpoint of further improving the intermittent ejection stability of the ink. , More preferably 20% by mass or more, still more preferably 25% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less, and still more preferably. 35% by mass or less.

(Content of wax emulsion (C))
The content of the wax emulsion (C) in the ink is preferably 0.1 mass as a solid content in the ink from the viewpoint of the stability of the wax emulsion in the ink, and from the viewpoint of improving the fixing property and the print image quality. % Or more, more preferably 0.5% by mass or more, further preferably 1% by mass or more, and from the viewpoint of further improving the intermittent discharge stability, preferably 6% by mass or less, more preferably 5% by mass or less, Preferably it is 3 mass% or less, More preferably, it is 2 mass% or less.
The content of the anionic wax emulsion (c-1) in the ink is preferably as a solid content in the ink from the viewpoint of the stability of the wax emulsion in the ink, and from the viewpoint of improving the fixability and print image quality. Is 0.05% by mass or more, more preferably 0.3% by mass or more, and further preferably 0.5% by mass or more. From the viewpoint of further improving the intermittent discharge stability, it is preferably 6% by mass or less, more preferably Is 5% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, and still more preferably 1.5% by mass or less.
The mass ratio [(B) / (C)] of the organic solvent (B) and the wax emulsion (C) further improves the storage stability and intermittent ejection stability of the ink, from the viewpoint of improving the fixing property and the print image quality. , Preferably 20 or more, more preferably 25 or more, still more preferably 28 or more, and preferably 50 or less, more preferably 45 or less, still more preferably 42 or less.

(Content of surfactant (D))
The content of the surfactant (D) in the ink is preferably 0.1% from the viewpoint of suppressing an increase in the ink viscosity, further improving the intermittent ejection stability of the ink, and improving the fixing property and the print image quality. % Or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2.5% by mass. It is as follows.
(Water content)
The content of water in the ink is preferably 20% by mass or more, more preferably 30% by mass or more, from the viewpoint of further improving the intermittent ejection stability and storage stability of the ink and improving the fixability and print image quality. More preferably, it is 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, and still more preferably 60% by mass or less.

(Other ingredients)
In the ink of the present invention, in addition to the above components, surfactants other than the commonly used humectants, wetting agents, penetrating agents, dispersants, acetylene glycol surfactants, viscosity modifiers, antifoaming agents, preservatives Various additives such as an antifungal agent and an antirust agent can be added.

  The aqueous ink of the present invention is obtained by mixing and stirring the pigment (A), the organic solvent (B), the wax emulsion (C), water, and other components such as a surfactant (D) as necessary. Can be obtained.

(Ink properties)
The viscosity of the ink at 32 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, and further preferably 5.0 mPa · s, from the viewpoint of improving the intermittent ejection stability of the ink. s or more, and preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, and even more preferably 7.0 mPa · s or less.
The pH of the ink is preferably 7.0 or more, more preferably 8.0 or more, from the viewpoint of improving the storage stability and intermittent ejection stability of the ink, and improving the fixability and print image quality. Preferably it is 8.5 or more. Moreover, from a viewpoint of member tolerance and skin irritation, pH becomes like this. Preferably it is 11.0 or less, More preferably, it is 10.0 or less, More preferably, it is 9.5 or less.
The viscosity and pH of the ink are measured by the method described in the examples.

[Inkjet printing method]
The inkjet printing method of the present invention is an inkjet printing method for discharging the aqueous ink of the present invention from a discharge nozzle of an inkjet print head onto a print medium, wherein the inkjet print head method is a line head method, and the printing speed is The amount of water absorption of the print medium is 0 g / m ² or more and 10 g / m ² or less at a contact time of 100 msec between the print medium and pure water in terms of the conveyance speed of the print medium.
The line head type inkjet print head is a long print head about the width of the print medium. The print head is fixed, the print medium is moved in the transport direction, and the nozzle opening of the print head is interlocked with this movement. By ejecting ink droplets from the ink and attaching them to a print medium, it is possible to print an image or the like at high speed.
Examples of the printing medium include liquid-absorbing printing media such as plain paper and high-quality paper, low liquid-absorbing printing media such as art paper and coated paper, and non-liquid-absorbing printing media such as synthetic resin films. The print medium is preferably roll paper.
The water-based ink of the present invention has excellent fixability even if it is a low liquid-absorbing or non-liquid-absorbing printing medium in which the ink is slowly absorbed or not absorbed, and thus the pigment tends to remain on the surface of the printing surface. In addition, since the printed material having the image quality can be obtained, the print medium used in the method of the present invention has a water absorption amount of 0 g / m ² or more at a contact time of 100 msec between the print medium and pure water. / M ² or less, preferably 5 g / m ² or less. The amount of water absorption can be measured by the method described in Examples using an automatic scanning liquid absorption meter.

  Since the water-based ink of the present invention can maintain intermittent ejection stability even in high-speed printing, the printing speed is 70 m / min or more, preferably 72 m / min or more in terms of the conveyance speed of the printing medium. The conveyance speed of the print medium is a movement speed with respect to the moving direction of the print medium. The printing speed is preferably 500 m / min or less, more preferably 300 m / min or less, and still more preferably 150 m / min or less from the viewpoint of drying an image or the like on the printed material.

The ink droplet ejection method is preferably a piezo method, but a thermal method can also be adopted.
The applied voltage of the print head is preferably 5 V or higher, more preferably 10 V or higher, still more preferably 15 V or higher, and preferably 40 V or lower, more preferably 35 V or lower, from the viewpoint of high-speed printing efficiency or the like. Preferably it is 30V or less.
The driving frequency is preferably 1 kHz or more, more preferably 5 kHz or more, still more preferably 10 kHz or more, and preferably 50 kHz or less, more preferably 40 kHz or less, still more preferably 35 kHz, from the viewpoint of high-speed printing efficiency or the like. It is as follows.
The amount of ink ejected droplets is preferably 30 pL or less, more preferably 20 pL or less, and even more preferably 10 pL per droplet from the viewpoint of maintaining the accuracy of the ink droplet landing position and improving the printing image quality. Hereinafter, it is more preferably 8 pL or less, and preferably 0.5 pL or more, more preferably 1 pL or more, still more preferably 1.5 pL or more, and still more preferably 2 pL or more.

  The printing resolution is preferably 200 dpi or more, more preferably 300 dpi or more, and preferably 1200 dpi or less, more preferably 1000 dpi or less, and still more preferably 800 dpi or less. Here, “printing resolution” in the present invention refers to the number of dots per inch (2.54 cm) formed on a printing medium. For example, “printing resolution is 600 dpi” means that ink droplets are ejected onto a printing medium using a line head in which the number of nozzle holes per inch of a nozzle row is arranged at 600 dpi (dots / inch). Corresponding rows of dots of 600 dpi per inch are formed in a direction perpendicular to the conveyance direction of the print medium. When ink droplets are ejected while moving the print medium in the transport direction, a line of dots of 600 dpi per inch is also formed on the print medium in the transport direction. In the present invention, the recording resolution in the direction perpendicular to the conveyance direction of the print medium and the recording resolution in the conveyance direction are expressed as the same value.

The temperature in the discharge head during printing, preferably in the line head, is preferably 20 ° C. or higher, more preferably 25 ° C. or higher, and still more preferably 30 from the viewpoint of lowering the viscosity of the ink and further improving the intermittent discharge stability. And is preferably 45 ° C. or lower, more preferably 40 ° C. or lower, and still more preferably 38 ° C. or lower.
The surface of the print medium facing the area where the discharge head, preferably the line head discharges ink, is preferably 28 ° C. or higher, more preferably 30 ° C. or higher, still more preferably 31 ° C. or higher, and preferably 45 ° C. or lower. More preferably, it is 40 ° C. or less, and more preferably 38 ° C. or less.
The adhesion amount of the ink on the print medium is preferably 0.1 g / m ² or more, and preferably 25 g / m ² or less, and more preferably, as a solid content from the viewpoint of improvement in print image quality and printing speed. 20 g / m ² or less.
In the ink jet printing method of the present invention, it is preferable to have a step of drying ink droplets that have landed on the print medium after the ink droplets have been ejected onto the print medium for printing.
In the drying step, the printing medium surface temperature is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, still more preferably 50 ° C. or higher, even more preferably 60 ° C. or higher, from the viewpoint of improving print quality. From the viewpoint of suppressing deformation of the printing medium by heat and reducing energy, it is preferably 200 ° C. or lower, more preferably 150 ° C. or lower, still more preferably 120 ° C. or lower, and still more preferably 90 ° C. or lower.

  In the following production examples, examples and comparative examples, “parts” and “%” are “parts by mass” and “mass%” unless otherwise specified.

(1) Measurement of weight average molecular weight of water-insoluble polymer Gel permeation was carried out using a solution in which phosphoric acid and lithium bromide were dissolved in N, N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. By a chromatography method [Tosoh Corporation GPC apparatus (HLC-8120GPC), Tosoh Corporation column (TSK-GEL, α-M × 2), flow rate: 1 mL / min], a single substance having a known molecular weight as a standard substance is used. Measured using dispersed polystyrene.

(2) Measurement of average particle diameter of pigment-containing polymer particles The measurement was performed by cumulant analysis 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 between incident light and a detector of 90 °, and the number of integrations of 100. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement concentration was 5 × 10 ⁻³ % (in terms of solid content concentration).

(3) Measurement of solid content concentration Weigh out 10.0 g of sodium sulfate constant in a desiccator into a 30 ml polypropylene container (φ = 40 mm, height = 30 mm) and add about 1.0 g of sample to it. After mixing, the sample was accurately weighed and maintained at 105 ° C. for 2 hours to remove volatile components, and further left in a desiccator for 15 minutes to measure the mass. The mass of the sample after removal of the volatile matter was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration.

(4) Measurement of melting point of wax The melting point of the wax was measured by a measuring device based on JIS K0064. Specifically, using a differential scanning calorimeter (Q20, manufactured by TA Instruments), the sample was heated to 200 ° C. and cooled from that temperature to 0 ° C. at a cooling rate of 10 ° C./min. Next, the sample was heated at a temperature rising rate of 10 ° C./min, and the heat quantity was measured up to 200 ° C. Of the observed heat of fusion peaks, the temperature of the peak with the largest peak area was taken as the maximum melting peak temperature, and the peak temperature was taken as the melting point.
(5) Measurement of average particle diameter of wax emulsion The average particle diameter (average dispersed particle diameter) of the wax emulsion was measured using a Microtrac particle size analyzer UPA manufactured by Nikkiso Co., Ltd.

(6) Measurement of viscosity of water-based ink Viscosity at 32 ° C. using E-type viscometer “TV-25” (manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1 ° 34 ′ × R24, rotation speed 50 rpm) Was measured.

(7) Measurement of pH of wax emulsion (C) and water-based ink A desktop pH meter “F-71” (manufactured by Horiba, Ltd.) using a pH electrode “6337-10D” (manufactured by Horiba, Ltd.) was used. The pH of the wax emulsion (C) and aqueous ink at 25 ° C. was measured.

(8) Measurement of water absorption amount of print medium The water absorption amount of the print medium at a contact time of 100 msec between the print medium and pure water is determined using an automatic scanning liquid absorption meter (KM500win, manufactured by Kumagaya Riki Kogyo Co., Ltd.) Under the conditions of 23 ° C. and 50% relative humidity, the amount of transition at a pure water contact time of 100 ms was measured as the amount of water absorption. 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 (Production of aqueous dispersion of pigment-containing polymer particles)
(1) Synthesis of water-insoluble polymer (1) 14 parts of methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.), 46 parts of styrene (manufactured by Wako Pure Chemical Industries, Ltd.), styrene macromonomer “AS-6S” (Toagosei Co., Ltd.) 30 parts by company, number average molecular weight 6,000, solid content 50%), 25 parts of polypropylene glycol methacrylate “Blenmer PP-1000” (NOF Corporation) and 25 parts of methyl ethyl ketone are mixed to prepare 140 parts of a monomer mixture. did.
In a reaction vessel, 18 parts of methyl ethyl ketone, 0.03 part of 2-mercaptoethanol which is a chain transfer agent, and 10% (14 parts) of the monomer mixture were mixed and sufficiently substituted with nitrogen gas.
On the other hand, the remaining 90% (126 parts) of the monomer mixture, 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. ”(Made by Wako Pure Chemical Industries, Ltd.) 3 parts of the mixed solution was put into a dropping funnel, and the temperature was raised to 75 ° C. while stirring the mixed solution in the reaction vessel in a nitrogen atmosphere, and the mixed solution in the dropping funnel Was added dropwise over 3 hours. After 2 hours at 75 ° C. from the end of dropping, a solution in which 3 parts of the polymerization initiator was dissolved in 5 parts of methyl ethyl ketone was added, and the mixture was further aged at 75 ° C. for 2 hours and 80 ° C. for 2 hours to give water-insoluble polymer (1) ( A weight average molecular weight: 60,000) solution was obtained. The solid concentration of the water-insoluble polymer solution was 60%.

(2) Production of aqueous dispersion of pigment-containing polymer particles 37 parts of water-insoluble polymer (1) obtained by drying the water-insoluble polymer solution obtained in (1) under reduced pressure was dissolved in 148 parts of methyl ethyl ketone, 12.5 parts of 5N aqueous sodium hydroxide solution, 2 parts of 25% aqueous ammonia and 372 parts of ion-exchanged water were added as neutralizing agents, and C.I. I. 100 parts of Pigment Blue 15: 3 (PB15: 3, manufactured by Dainichi Seika Kogyo Co., Ltd.) was added to obtain a pigment mixture. The degree of neutralization was 100 mol%. The pigment mixture was mixed for 1 hour under conditions of 7,000 rpm and 20 ° C. using a disper blade. 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).
The resulting dispersion of the pigment-containing polymer particles is subjected to removal of methyl ethyl ketone at 60 ° C. under reduced pressure, further removing a part of water, centrifuging, and filtering the liquid layer portion with a filter “Mini Sarto Syringe Filter” (Sartorius) Manufactured, pore size: 5 μm, material: cellulose acetate) to remove coarse particles to obtain an aqueous dispersion of pigment-containing polymer particles. The solid content concentration was 20%, and the average particle size of the pigment-containing polymer particles was 100 nm.

Example 1 (Production of water-based ink)
24 parts of an aqueous dispersion (solid content 20%) of pigment-containing polymer particles obtained in Production Example 1 (3.5 parts of pigment, 1.3 parts of water-insoluble polymer (1)), 40 parts of propylene glycol, acetylene glycol type Surfactant (product name: Surfinol 465, manufactured by Air Products & Chemicals, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethylene oxide 10 mol adduct) 1.5 parts , 1 part of wax emulsion (product name: AQUACER 507, manufactured by BYK, solid content 30%), appropriate amount of 1N NaOH aqueous solution so that pH is 9, and ion-exchanged water are added and mixed so that the total amount becomes 100 parts did. The obtained mixed solution was filtered through a filter “Mini-Salto syringe filter” (manufactured by Sartorius, pore size: 1.2 μm, material: cellulose acetate) to obtain an aqueous ink having a viscosity of 5.5 and a pH of 9.

Examples 2-7, Comparative Examples 1-9 (Production of water-based ink)
A water-based ink was prepared in the same manner as in Example 1 except that the organic solvent and the wax emulsion shown in Tables 1 and 2 were used and the blending compositions shown in Tables 1 and 2 were used. Got.

Each component shown in Table 1 and Table 2 is as follows.
[Organic solvent: Wako Pure Chemical Industries, Ltd.]
・ Propylene glycol (boiling point 188 ℃)
・ 1,5-pentanediol (boiling point 239 ° C.)
・ 1,2-butanediol (boiling point 194 ° C.)
・ 1,2-hexanediol (boiling point 223 ° C)
・ Glycerin (boiling point 290 ° C)
・ Isopropyl alcohol (boiling point 82 ℃)
2-pyrrolidone (boiling point 245 ° C)

(Wax emulsion)
AQUACER 507 (anionic emulsion of oxidized high-density polyethylene wax, melting point 130 ° C., pH 9.7, average particle size 50 nm, manufactured by BYK)
AQUACER 537 (anionic emulsion of modified paraffin wax, melting point 110 ° C., pH 9.5, average particle size 61 nm, manufactured by BYK)
AQUACER 1547 (an anionic emulsion of oxidized high-density polyethylene wax, melting point 125 ° C., pH 9.7, average particle size 70 nm, manufactured by BYK)
PEM-17 (anionic emulsion of polyethylene wax, melting point 105 ° C., pH 11, average particle size 40 nm, manufactured by San Nopco)
Chemipearl W4005 (self-dispersing emulsion of low molecular weight polyethylene wax, melting point 110 ° C., pH 11, average particle size 600 nm, manufactured by Mitsui Chemicals, Inc.)
AQUACER 515 (nonionic emulsion of oxidized high-density polyethylene wax, melting point 135 ° C., pH 9.5, average particle size 100 nm, manufactured by BYK)
AQUACER 526 (anionic emulsion of modified ethylene vinyl acetate wax, melting point 105 ° C., pH 9.7, average particle size 30 nm, manufactured by BYK)
In addition, the compounding quantity of the wax emulsion (C) in Table 1 and Table 2 is the quantity (part) as solid content.

<Evaluation test of water-based ink>
Preparation Example 1 (Preparation of inkjet print)
Implemented in a WEB printing evaluation system (manufactured by Tritech Co., Ltd.) equipped with an inkjet printing line head “KJ4B-Z series” (manufactured by Kyocera Corporation) in an environment with a temperature of 25 ± 1 ° C. and a relative humidity of 30 ± 5%. The aqueous inks obtained in Examples and Comparative Examples were filled.
The line head applied voltage was 26 V, the ejection droplet amount was 7 pL, the printing resolution was 600 dpi, the pre-ejection flushing count was 200, the negative pressure was -4.0 kPa, and the roll paper conveyance speed (printing speed) was set to 75 m / min.
As a roll paper print medium, a print medium ("UPM Finesse Gloss" (manufactured by UPM), water absorption of 3.1 g / m ² ) is set in a print evaluation machine, and a print command is transferred to the print evaluation apparatus. The ink was solid-printed on a printing medium by an inkjet recording method. Further, immediately after the printing, a hot air dryer (set temperature 60 ° C.) was passed through to produce a printed matter, and the following evaluation tests 1 to 4 were performed. The results are shown in Tables 1 and 2.

Test 1 (intermittent discharge stability: discharge recovery rate (%))
After preparing the inkjet print, the printing machine was stopped for 30 minutes and the print line head was exposed to the atmosphere. After the lapse of 30 minutes, the discharge state of the first solid printed material when printing was resumed was observed, the discharge recovery rate (%) was calculated by the following formula, and the intermittent discharge stability was evaluated.
(Evaluation criteria)
Discharge recovery rate (%) = (Discharge area of solid printing after exposure to air for 30 minutes / Discharge area of solid printing before test) × 100
As the discharge recovery rate (%) is larger, it is judged that the intermittent discharge stability is better, and if it is 70% or more, it can be put to practical use.

Test 2 (print quality)
The solid image of the printed matter obtained in Preparation Example 1 was observed, the presence or absence of mottling was visually confirmed, and the print image quality was evaluated according to the following evaluation criteria.
(Evaluation criteria)
4: Mottling cannot be visually confirmed.
3: Although mottling can be confirmed, it can be used practically.
2: Mottling can be confirmed and cannot be used practically.
1: Mottling can be confirmed strongly and cannot be used practically.

Test 3 (Fixability)
Visually confirm the decrease in print area before and after printing media conveyance using a stainless steel metal conveyance roller installed on the printing evaluation machine, calculate the transfer resistance (%) by the following formula, and evaluate the fixability did.
(Evaluation criteria)
Transfer resistance (%) = (printing area after roller conveyance / printing area before roller conveyance) × 100
As the transfer resistance (%) is larger, it is judged that the roller image can be suppressed, and the fixing property is excellent. If it is 70% or more as a numerical value, it can be used practically.

Test 4 (storage stability)
The prepared ink was subjected to a storage test in a sealed container at 70 ° C. in a constant temperature room. One week later, each was taken out, the viscosity (E-type viscometer) was measured, and the rate of change in viscosity was calculated by the following formula (the fractional part was rounded down). About the obtained viscosity change rate, the storage stability was evaluated according to the following evaluation criteria. If it is 3 or more according to the following evaluation criteria, it can be used practically.
Viscosity change rate (%) = 100 − [(viscosity after storage) / (viscosity before storage)] × 100
(Evaluation criteria)
4: Viscosity change rate after 1 week at 70 ° C. is less than 5%.
3: Viscosity change rate after 1 week at 70 ° C. is 5% or more and less than 10%.
2: The viscosity change rate after 1 week at 70 ° C. is 10% or more and less than 20%.
1: The ink loses fluidity and is not at a level where the viscosity can be measured.

From Tables 1 and 2, the inks of Examples 1 to 7 achieve storage stability, intermittent ejection stability, excellent fixing properties and image quality at a high level in a balanced manner as compared with the inks of Comparative Examples 1 to 9. I understand that.
Since Comparative Example 1 does not contain the anionic wax emulsion (c-1), the intermittent ejection stability is inferior.
In Comparative Example 2, since the wax emulsion (C) does not contain a wax having a melting point of 110 ° C. or higher, the intermittent ejection stability is inferior.
In Comparative Example 3, since the average particle size of the wax emulsion (C) is more than 400 nm, the storage stability, intermittent ejection stability, and print image quality are inferior.
Since Comparative Example 4 does not use the wax emulsion (C), the fixability is inferior.
Since Comparative Examples 5 to 9 do not contain alkanediol (b-1) having 5 or less carbon atoms, any of storage stability, intermittent ejection stability, image quality, and fixability is inferior.

  Since the water-based ink of the present invention is excellent in storage stability, it can be suitably used as a flexographic ink, a gravure ink, or an inkjet ink. In addition, a printed matter obtained by using a low-absorbing print medium while maintaining intermittent ejection stability has excellent fixability and image quality, and therefore can be used particularly as an ink for ink jet printing.

Claims (5)

A water-based ink containing a pigment (A), an organic solvent (B), a wax emulsion (C) and water,
The organic solvent (B) contains an alkanediol (b-1) having 5 or less carbon atoms,
The wax emulsion (C) includes an anionic wax emulsion (c-1), and the content of the anionic wax emulsion (c-1) in the wax emulsion (C) is 50% by mass or more,
The wax emulsion (C) contains at least one wax having a melting point of 110 ° C. or higher,
A water-based ink in which the average particle size of the wax emulsion (C) is 400 nm or less.   2. The water-based ink according to claim 1, wherein the content of the wax having a melting point of 110 ° C. or more is 50% by mass or more in the total amount of the wax contained in the wax emulsion (C).   The water-based ink according to claim 1 or 2, wherein the wax emulsion (C) has an average particle size of 10 nm or more.   The aqueous ink according to any one of claims 1 to 3, wherein the content of the organic solvent (B) is 10% by mass or more and 50% by mass or less in the aqueous ink. An inkjet printing method for discharging the water-based ink according to any one of claims 1 to 4 from a discharge nozzle of an inkjet print head onto a print medium,
The inkjet print head system is the line head system,
The printing speed is 70 m / min or more in terms of the conveyance speed of the printing medium,
An ink-jet printing method, wherein a water absorption amount of the print medium at a contact time of 100 msec between the print medium and pure water is from 0 g / m ^{2 to} 10 g / m ² .