JP6819995B2 - Water-based ink - Google Patents

Description

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

The inkjet printing method is a printing method in which ink droplets are directly ejected from a fine nozzle and adhered to a printing medium to obtain a printed matter on which characters and images are recorded. This method has the advantages of easy and inexpensive full-color printing and non-contact with the printed matter. Therefore, this method is not limited to consumer printing for general consumers, and in recent years, it has been used for analog printing such as offset printing and gravure printing. It is beginning to be applied to the commercial printing and industrial printing fields that have been practiced.
The advantage of developing inkjet printing in the fields of commercial printing and industrial printing is that it does not require a printing plate unlike analog printing, so it can handle small quantities and on-demand printing such as variable printing.

In the fields of commercial printing and industrial printing, high-speed printing is performed because higher productivity is required compared to consumer printing. In order to support this high-speed printing, a line head type print head has been developed. In the conventional serial head method, the head (nozzle) is operated a plurality of times to print, whereas in the line head method, the head is fixed and only the printing roll paper is scanned, so that high-speed printing is possible. On the other hand, in the line head method, since the head passes through the paper only once, if ink ejection failure occurs even with one nozzle, the image quality is immediately deteriorated, so that the ejection stability is higher. Sex is required.
For example, in Patent Document 1, in order to improve the intermittent ejection property of ink when printing on sheet paper by using the serial head method, specific compounds such as pigments, polymer dispersants, and polypropylene glycols 0.01 to 0.01 to Water-based pigment inks containing 3% by weight, a water-soluble solvent, and water are disclosed.
Patent Document 2 describes a pigment coated with a water-insoluble resin and water-insoluble with a glass transition temperature of 100 ° C. or higher in order to have excellent ink ejection property and maintainability and to suppress the occurrence of 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.

Further, in the fields of commercial printing and industrial printing, in addition to printing on conventional plain paper, high-liquidity recording medium called copy paper, low-liquidity coated paper such as offset coated paper, or polypropylene resin, Printing of non-liquid absorbing resin such as polyester resin on a recording medium such as a film is required. In these low-liquid absorption or non-liquid absorption recording media, since the pigment is present on the surface of the printing surface, the printing surface comes into contact with a transport roller or the like in the printing machine, and the pigment is scraped off by the roller and transferred. There is a problem that so-called roller transfer occurs, the print area is reduced, and the image quality is deteriorated.

Japanese Unexamined Patent Publication No. 10-53741 Japanese Unexamined Patent Publication No. 2011-162692

In the water-based pigment ink of Patent Document 1 and the ink composition of Patent Document 2, the suppression of the roller image of the pigment is insufficient, and improvement thereof is desired. Wax is used in the ink composition of Patent Document 2, but the melting point of the wax specifically used in the examples is 102 ° C. at the maximum.
The present invention is excellent in storage stability of water-based ink, and while ensuring ejection stability (intermittent ejection stability) in high-speed printing by an inkjet recording method, a pigment roller can be used even when a recording medium having low liquid absorption is used. An object of the present invention is to provide a water-based ink capable of suppressing image reflection and an inkjet 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 amount of water absorption of the recording medium in a contact time of 100 msec between the recording medium and pure water is It means that it is 0 g / m ² or more and 10 g / m ² or less.

The present inventors have excellent storage stability, and even in high-speed printing at a printing speed of 70 m / min or more, excellent intermittent ejection is achieved by using polypropylene glycol as a moisturizer and a wax emulsion containing a wax that is difficult to melt. It has been found that it is possible to obtain a water-based ink capable of suppressing the roller image of the pigment while maintaining the stability. By using a wax having a melting point of 108 ° C. or higher, it is considered that the intermittent discharge stability is maintained because the wax does not melt in the vicinity of the discharge nozzle.
That is, the present invention provides the following [1] and [2].
[1] A water-based ink containing a pigment (A), a polypropylene glycol (B), an organic solvent (C), a wax emulsion (D), and water, and the melting point of the wax contained in the wax emulsion (D) is 108 ° C. The above water-based ink.
[2] An inkjet printing method in which the water-based ink according to the above [1] is ejected from an ejection nozzle of an inkjet printing head onto a printing medium.
The method of the inkjet printing head is the line head method,
The printing speed is 70 m / min or more in terms of the transport speed of the printing medium.
An inkjet printing method in which the water absorption 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, a water-based ink having excellent storage stability of the water-based ink and capable of suppressing roller transfer of pigments while maintaining high ejection stability even in high-speed printing by an inkjet recording method, and the water-based ink are used. An inkjet printing method can be provided.

[Aqueous 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), polypropylene glycol (B), an organic solvent (C), a wax emulsion (D), and water. The melting point of the wax contained in the wax emulsion (D) is 108 ° C. or higher.
The term "water-based" means that water accounts for the largest proportion of 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 an ink for flexo printing, an ink for gravure printing, or an ink for an inkjet, and an inkjet recording method. Since it is possible to suppress the roller image of the pigment while maintaining the high intermittent ejection stability in the above, it is particularly preferable to use it as an ink for an inkjet.

When the water-based ink of the present invention is used, the roller image of the pigment can be transferred while maintaining the intermittent ejection stability of the ink after a predetermined time has elapsed without ejecting the ink from the ejection nozzle in the inkjet recording method even in high-speed printing. It can be suppressed and has the effect of excellent storage stability of water-based ink. The reason is not clear, but it can be considered as follows.
In printing using water-based ink, the frequency of use differs for each nozzle, and in the case of nozzles that are used less frequently, the ink dries more and more easily solidifies. Further, on a low liquid absorption printing medium, the pigment is left on the surface of the printing surface because the ink is absorbed slowly or is not absorbed.
Here, in the present invention, by adding polypropylene glycol (B) as a moisturizer to the ink, drying of the ink is suppressed, ejection failure due to solidification of the ink is prevented, and the organic solvent (C) added to the ink is used. The total amount can be reduced. Further, by adding a wax emulsion (D) containing a wax having a melting point of 108 ° C. or higher, which is difficult to melt, it is possible to suppress destabilization of intermittent ejection of ink due to melting of wax particles in the vicinity of the ejection nozzle. It is considered that this can be done and the roller image of the pigment at the time of printing can be suppressed. On the other hand, if the melting point of the wax is less than 108 ° C., during intermittent printing, the wax is repeatedly melted (or softened) and solidified in the vicinity of the discharge nozzle, and the wax emulsion is aggregated and deformed and further adheres to the nozzle member. Is considered to cause instability of intermittent discharge.
Further, even if polypropylene glycol (B) and wax emulsion (D) are used in combination, the wax emulsion (D) containing wax having a melting point of 108 ° C. or higher is less susceptible to plasticization and dispersion instability due to polypropylene glycol (B). Even in high-speed printing, more excellent intermittent ejection stability and storage stability can be exhibited.

<Water-based ink>
The water-based ink of the present invention contains a pigment (A), polypropylene glycol (B), an organic solvent (C), a wax emulsion (D) 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. In addition, if necessary, they can be used in combination with extender pigments.
Specific examples of the inorganic pigment include carbon black and metal oxides, and carbon black is particularly preferable for black ink. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Specific examples of the 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 preferable 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.
Examples of the extender pigment include silica, calcium carbonate, talc and the like.

The pigment (A) is 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) further improves the storage stability and intermittent ejection stability of the ink, and from the viewpoint of suppressing the roller image of the pigment, the water-insoluble polymer particles containing the pigment (A) (hereinafter, simply "pigment-containing polymer"). It is preferably contained as "particles").

[Water-insoluble polymer particles containing pigments (pigment-containing polymer particles)]
(Water-insoluble polymer)
The water-insoluble polymer has a function as a pigment dispersant that exhibits a pigment dispersion action and a function as a fixing agent on a printing medium.
Here, "water-insoluble" means that the amount of the polymer that has reached a constant weight after being dried at 105 ° C. for 2 hours is 10 g or less when it is dissolved in 100 g of water at 25 ° C. 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 dissolved amount is the dissolved amount when the anionic group of the polymer is 100% neutralized with sodium hydroxide. When the water-insoluble polymer is a cationic polymer, the dissolved amount is the dissolved amount when the cationic group of the polymer is 100% neutralized with hydrochloric acid.
The water-insoluble polymer exists in the ink in a state of being adsorbed on the pigment, a state of containing the pigment (capsule), and a state of not adsorbing the pigment. 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-containing state containing the pigment is more preferable.
Examples of the polymer used include polyester, polyurethane, and vinyl-based polymers. From the viewpoint of improving the storage stability of the ink, vinyl-based polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds) are used. Polymers are preferred.

As the vinyl-based polymer, a monomer mixture containing (a) an ionic monomer (hereinafter, also referred to as “(a) component”) and (b) a hydrophobic monomer (hereinafter, also referred to as “(b) component”) ( Hereinafter, a vinyl-based polymer obtained by copolymerizing a "monomer mixture") is preferable. This vinyl-based polymer has a structural unit derived from the component (a) and a structural unit derived from the component (b). Among them, those further containing a structural unit derived from (c) macromonomer (hereinafter, also referred to as “component (c)”) are preferable.

[(A) Ionic monomer]
The (a) 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. The ionic monomer includes a monomer that becomes an ion under acidic or alkaline conditions even if it is a monomer that is not an ion in a neutral state 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-methacryloyloxymethylsuccinic acid.
Among the anionic monomers, 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 cationic monomer include N, N-dimethylaminoethyl methacrylate, N, N-dimethylaminoethyl acrylamide and the like.

[(B) Hydrophobic monomer]
(B) 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 an alkyl (meth) acrylic acid ester and an aromatic group-containing monomer.
The alkyl (meth) acrylic acid ester preferably has an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and is preferably, for example, methyl (meth) acrylate, ethyl (meth) acrylate, or (iso) propyl. (Meta) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, ( Examples thereof include iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, and (iso) stearyl (meth) acrylate.
In addition, "(iso or tertiary)" and "(iso)" mean both the case where these groups are present and the case where these groups are not present, and when these groups are not present, they indicate normal. Further, "(meth) acrylic acid" means one or more kinds selected from acrylic acid and methacrylic acid, and "(meth) acrylic acid ester" means one kind selected from acrylic acid ester and methacrylic acid ester. It 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 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.
Further, 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.
As the hydrophobic monomer (b), two or more of the above-mentioned monomers may be used, or a styrene-based monomer and an aromatic group-containing (meth) acrylic acid ester may be used in combination.

[(C) Macromonomer]
(C) 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, and is a water-insoluble polymer from the viewpoint of improving the dispersion stability of pigment-containing polymer particles in ink. It is preferable to use it as a monomer component of. As the polymerizable functional group present at one end, an acryloyloxy group or a methacryloyloxy group is preferable, and a methacryloyloxy group is more preferable.
(C) 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 a gel permeation chromatography method using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
As the macromonomer, aromatic group-containing monomer-based macromonomers and silicone-based macromonomers are preferable, and aromatic group-containing monomer-based macromonomers are preferable from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink. More preferable.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomer described in (b) Hydrophobic Monomer, and styrene and benzyl (meth) acrylate are preferable, and styrene is preferable. More preferable.
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.
Examples of the silicone-based macromonomer include organopolysiloxane having a polymerizable functional group at one end.

[(D) Nonionic monomer]
For the water-insoluble polymer, from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the ink, (d) a nonionic monomer (hereinafter, also referred to as “(d) component”) may be used as the monomer component. preferable.
As the component (d), 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (n = 2 to 30, n indicates the average number of moles of oxyalkylene group added; the same applies hereinafter). Polyalkylene glycol (meth) acrylate such as (meth) acrylate and polyethylene glycol (n = 2 to 30) (meth) acrylate, alkoxy polyalkylene glycol (meth) such as methoxypolyethylene glycol (n = 1 to 30) (meth) acrylate. ) Acrylate, phenoxy (ethylene glycol-propylene glycol copolymerization) (n = 1 to 30, ethylene glycol: n = 1 to 29) (meth) acrylate and the like can be mentioned.

Specific examples of the commercially available component (d) include Shin Nakamura Chemical Industry Co., Ltd.'s NK Ester M-20G, 40G, 90G, 230G, etc., NOF Corporation's Blemmer PE-90, and the same. 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 so on.
The above components (a) to (d) can be used alone or in combination of two or more.

(Content of each component or structural unit in the monomer mixture or polymer)
The content of the components (a) and (b) in the monomer mixture during the production of the water-insoluble polymer (content as an unneutralized amount; the same applies hereinafter) or the components (a) and (b) in the water-insoluble polymer. The content of the structural unit derived from 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) is preferably 5% by mass or more, more preferably 8% by mass or more, further preferably 10% by mass or more, and preferably 45% by mass or less, more preferably 35% by mass or less. , More preferably 30% by mass or less.
The content of the component (b) is preferably 35% by mass or more, more preferably 40% by mass or more, further preferably 45% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less. , More preferably 75% by mass or less.

Further, the content of the components (a) to (d) in the monomer mixture or (a) to (a) in the water-insoluble polymer at the time of producing the water-insoluble polymer when the components (c) and / or (d) are contained. d) The content of the structural unit derived from the component 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) is preferably 3% by mass or more, more preferably 5% by mass or more, further preferably 7% 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 (b) 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.
When the component (c) is contained, the content of the component (c) 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 more. Below, it is more preferably 25% by mass or less, still more preferably 20% by mass or less.
When the component (d) is contained, the content of the component (d) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 40% by mass or more. Below, it is more preferably 35% by mass or less, still more preferably 30% by mass or less.
The mass ratio of [component (a) / component (b)] is preferably 0.05 or more, more preferably 0.15 or more, still more preferably 0.25 or more, and preferably 1.2 or less. It is more preferably 0.80 or less, still more preferably 0.50 or less.
When the component (c) is contained, the mass ratio of [(a) component / [(b) component + (c) component]] is preferably 0.01 or more, more preferably 0.05 or more, and further. It is preferably 0.10 or more, and preferably 1 or less, more preferably 0.60 or less, still more preferably 0.40 or less.

(Manufacturing of water-insoluble polymer)
The water-insoluble polymer is produced by copolymerizing a monomer mixture by a known polymerization method such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Of these polymerization methods, the solution polymerization method is preferable.
The solvent used in the solution polymerization method is not limited, but polar organic solvents such as fatty alcohols having 1 to 3 carbon atoms, ketones, ethers, and esters are preferable, and specifically, methanol, ethanol, acetone, and methyl ethyl ketone are preferable. Methyl ethyl ketone is preferred.
At the time of polymerization, a polymerization initiator or a polymerization chain transfer agent can be used, but 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.

Preferred polymerization conditions differ depending on the type of polymerization initiator and the like, but 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 lower. 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 and solvent distillation. In addition, unreacted monomers and the like can be removed from the obtained polymer by reprecipitation, membrane separation, chromatographic method, extraction method and the like.
From the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing polymer particles described later, the water-insoluble polymer can be used as an organic solvent used in step I described later without removing the solvent used in the polymerization reaction. For use, it is preferable to use it as it is as a water-insoluble polymer solution.
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 preferably 70% by mass from the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing polymer particles. % 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, the storage stability and the intermittent ejection stability of the ink, and the roller image of the pigment is transferred. From the viewpoint of suppressing the above, it is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 20,000 or more, and preferably 500,000 or less, more preferably 400,000 or less, still more preferably. Is 300,000 or less, more preferably 200,000 or less.
The weight average molecular weight can be measured by the method described in Examples.

[Manufacture of pigment-containing polymer particles]
The water-based ink of the present invention can contain water-insoluble polymer particles containing the pigment (A).
The water-insoluble polymer particles containing the pigment (A) (pigment-containing polymer particles) can be efficiently produced by a method having the following steps I and II as an aqueous dispersion.
Step I: A mixture containing a water-insoluble polymer, an organic solvent, a pigment (A), and water (hereinafter, also referred to as "pigment mixture") is dispersed to obtain a dispersion of pigment-containing polymer particles. Step II: A step of 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 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, a surfactant, and the like are added to the obtained organic solvent solution and mixed. However, a method of obtaining an oil-in-water type dispersion is preferable. The order of adding the water-insoluble polymer to the organic solvent solution is not limited, but it is preferable to add water, the neutralizing agent, and the pigment (A) in this order.
The organic solvent for dissolving the water-insoluble polymer is not limited, but aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, esters and the like are preferable, and the wettability to the pigment (A) and the dissolution of the water-insoluble polymer are preferable. From the viewpoint of improving the properties and the adsorptivity of the water-insoluble polymer to the pigment (A), a ketone having 4 or more and 8 or less carbon atoms is more preferable, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is even more preferable.
When the water-insoluble polymer is synthesized by the 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, a neutralizing agent may be used to neutralize the anionic groups in the water-insoluble polymer. When a neutralizing agent is used, it is preferable to neutralize the pH so that the pH is 7 or more and 11 or less.
Examples of the neutralizing agent include alkali metal hydroxides, ammonia, organic amines and the like. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide, but sodium hydroxide is preferable. Examples of the organic amine include trimethylamine, ethylamine, diethylamine, triethylamine, triethanolamine and the like.
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 sodium hydroxide and ammonia in combination. Moreover, the water-insoluble polymer may be neutralized in advance.
The neutralizing agent is preferably used as an aqueous solution of the neutralizing agent 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, further preferably 15% by mass or more, and preferably 30% by mass or less, preferably 25% by mass or less. More preferred.
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 the ink. It is mol% or more, more preferably 50 mol% or more, preferably 300 mol% or less, more preferably 200 mol% or less, still more preferably 150 mol% or less.
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 pigment mixture)
The content of the pigment (A) in the pigment mixture in the step I further improves the dispersion stability of the pigment aqueous dispersion, the storage stability of the ink, and the intermittent ejection stability, and makes the pigment roller image. From the viewpoint of suppression, it is preferably 10% by mass or more, more preferably 12% by mass or more, further preferably 14% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably. It is 20% by mass or less.
The content of the water-insoluble polymer in the pigment mixture is from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, further improving the storage stability and intermittent ejection stability of the ink, and suppressing the roller image of the pigment. It is preferably 2.0% by mass or more, more preferably 4.0% by mass or more, further preferably 5.0% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, further. It is preferably 10% by mass or less.
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. It is more preferably 15% by mass or more, preferably 35% by mass or less, more preferably 30% by mass or less, 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, still more preferably 45% by mass or more, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and improving the productivity. It is 50% by mass or more, preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less.

The mass ratio [(A) / (a)] of the pigment (A) to the water-insoluble polymer (a) in the pigment mixture is from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, and the storage stability and intermittentness of the ink. From the viewpoint of further improving the ejection stability and suppressing the roller image of the pigment, it is preferably 30/70 or more, more preferably 40/60 or more, further preferably 50/50 or more, and preferably 90/10 or more. Below, it is more preferably 80/20 or less, still more preferably 75/25 or less.

(Dispersion treatment of pigment mixture)
In step I, the pigment mixture is dispersed to obtain a dispersion of pigment-containing polymer particles. There is no particular limitation on the dispersion method for obtaining the dispersion. Although it is possible to atomize the average particle size of the pigment particles to a desired particle size only by the main dispersion, preferably, after the pigment mixture is pre-dispersed, the main dispersion is further applied by applying shear stress to perform the main dispersion of the pigment particles. It is preferable to control the average particle size of the above to a desired particle size.
The temperature in the pre-dispersion of step I is preferably 0 ° C. or higher, preferably 40 ° C. or lower, more preferably 30 ° C. or lower, still more preferably 25 ° C. or lower, and the dispersion time is preferably 0.5 hours. As described above, it is more preferably 0.8 hours or more, preferably 30 hours or less, more preferably 10 hours or less, and further preferably 5 hours or less.
When the pigment mixture is pre-dispersed, a commonly used mixing and stirring device such as an anchor blade and a discharge blade can be used, and a high-speed stirring and mixing device is particularly preferable.

Examples of means for applying the shear stress of this dispersion 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 type disperser such as a paint shaker and a bead mill. Examples of commercially available media-type dispersers include Ultra Apex Mill (manufactured by Kotobuki Kogyo Co., Ltd.) and Pico Mill (manufactured by Asada Iron Works Co., Ltd.). 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 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.
From the viewpoint of productivity and economy, the treatment pressure is preferably 60 MPa or more, more preferably 100 MPa or more, further preferably 130 MPa or more, and preferably 200 MPa or less, more preferably 180 MPa or less.
The number of passes is preferably 3 or more, more preferably 10 or more, and preferably 30 or less, more preferably 25 or less.

(Step II)
In step II, an aqueous dispersion of pigment-containing polymer particles (pigment aqueous dispersion) can be obtained by removing the organic solvent from the dispersion obtained in step I by a known method. It is preferable that the organic solvent in the obtained aqueous pigment dispersion is substantially removed, but it 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 heat-stirred before distilling off the organic solvent.
The obtained pigment aqueous dispersion is one in which solid water-insoluble polymer particles containing the pigment (A) are dispersed in a medium containing water as a main medium. Here, the form of the pigment-containing polymer particles is not particularly limited, and it is sufficient that the particles are formed by 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) are 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 the preparation of ink. Is 15% by mass or more, preferably 30% by mass or less, and more preferably 25% by 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 75 nm, from the viewpoint of reducing coarse particles and further improving the intermittent ejection stability of the ink. It is more 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 Examples.
The average particle size of the pigment-containing polymer particles in the ink is the same as the average particle size in the pigment aqueous dispersion, and the preferred average particle size is the same as the average particle size in the pigment aqueous dispersion. It is the same.

<Polypropylene glycol (B)>
Polypropylene glycol (B) is used from the viewpoint of alleviating the agglutinating force of ink agglutinating deposits generated in the vicinity of the nozzle hole of the print head and further improving the intermittent ejection stability during high-speed printing.
Polypropylene glycol (B) is a polymer of propylene glycol and has a distribution composed of a plurality of components having different degrees of polymerization. The degree of polymerization of polypropylene glycol (B) is preferably 3 or more, more preferably 4 or more, still more preferably 5 or more, still more preferably, from the viewpoint of imparting appropriate viscosity to the ink and further improving the intermittent ejection stability. Is 6 or more, and is 30 or less, preferably 25 or less, more preferably 20 or less, still more preferably 15 or less.
The average molecular weight of polypropylene glycol (B) is preferably 250 or more, more preferably 300 or more, still more preferably 400 or more, still more preferably, from the viewpoint of imparting appropriate viscosity to the ink and further improving the intermittent ejection stability. Is 500 or more, and from the same viewpoint, it is preferably 2000 or less, more preferably 1800 or less, still more preferably 1600 or less, still more preferably 1400 or less.
The degree of polymerization of polypropylene glycol (B) can be measured and the average molecular weight can be calculated by the method described in Examples.

<Organic solvent (C)>
The organic solvent (C) is used from the viewpoint of improving the storage stability and the intermittent ejection stability of the ink.
From the same viewpoint as above, the boiling point of the organic solvent (C) is preferably 150 ° C. or higher, more preferably 160 ° C. or higher, further preferably 180 ° C. or higher, and preferably 250 ° C. or lower, more preferably 246 ° C. or higher. ° C. or lower, more preferably 215 ° C. or lower, even more preferably 210 ° C. or lower, still more preferably 200 ° C. or lower. When two or more kinds of organic solvents are used as the organic solvent (C), the weighted average value weighted by the content (mass%) of a plurality of organic solvents having different boiling points is preferably 150 ° C. or higher and 250 ° C. or lower. ..

Examples of the organic solvent (C) include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds and the like, and include polyhydric alcohols, polyhydric alcohol alkyl ethers and One or more selected from the nitrogen heterocyclic compound is preferable, and one or more selected from the polyhydric alcohol and the nitrogen-containing heterocyclic compound is more preferable.
The total content of one or more selected from the polyhydric alcohol, the polyhydric alcohol alkyl ether, and the nitrogen-containing heterocyclic compound in the organic solvent (C) is preferably 80% by mass or more, more preferably 90% by mass or more. 95% by mass or more is further preferable, and substantially 100% by mass is even more preferable.

Examples of the polyhydric alcohol include ethylene glycol (boiling point 197 ° C.), diethylene glycol (boiling point 244 ° C.), polyethylene glycol, propylene glycol (boiling point 188 ° C.), dipropylene glycol (boiling point 232 ° C.), polypropylene glycol, 1,3-. Propanediol (boiling point 210 ° 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), 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.
Further, polyhydric alcohols having a boiling point of more than 250 ° C. such as triethylene glycol (boiling point 285 ° C.), tripropylene glycol (boiling point 273 ° C.), and glycerin (boiling point 290 ° C.) are preferably polyhydric alcohols having a boiling point less than 250 ° C. Can be used in combination with polyhydric alcohols having a boiling point of less than 230 ° C. Among these, ethylene glycol, diethylene glycol and propylene glycol are preferable, and diethylene glycol and propylene glycol are more preferable, from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink and suppressing the roller image of the pigment.

Examples of the polyhydric alcohol alkyl ether include ethylene glycol monoethyl ether (boiling temperature 135 ° C.), ethylene glycol monobutyl ether (boiling point of 171 ° C.), diethylene glycol monomethyl ether (boiling point of 194 ° C.), and diethylene glycol monoethyl ether (boiling point of 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 Examples thereof include 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.), and ε-caprolactam (boiling point 220 ° C.). Boiling point 136 ° C.) and the like. Among these, N-methyl-2-pyrrolidone and 2-pyrrolidone are preferable.

Among the above organic solvents, from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink, it is preferable to contain at least one selected from diethylene glycol, propylene glycol and 2-pyrrolidone, and from diethylene glycol and propylene glycol. It is more preferable to contain one or more selected species.
Further, when printing on a recording medium having low water absorption, from the viewpoint of ejection property and ink drying property on paper, one or more polyhydric alcohols and one or more nitrogen-containing heterocyclic compounds or It is also preferable to use two or more kinds in appropriate combination.

<Wax emulsion (D)>
In the present invention, the wax emulsion (D) used has a melting point of 108 ° C. or higher for the wax contained therein, from the viewpoint of improving the storage stability and intermittent ejection stability of the ink and suppressing the roller image of the pigment. ..
The melting point of the wax contained in the wax emulsion (D) is preferably 110 ° C. or higher, more preferably 115 ° C. or higher, further preferably 120 ° C. or higher, and preferably 150 ° C. or lower, more preferably 145 ° C. or lower. More preferably, it is 140 ° C. or lower.
The melting point of the wax can be measured by the method described in Examples.

Examples of the wax emulsion (D) include wax emulsions containing polyolefin wax, paraffin wax, sazole wax and the like.
The polyolefin wax is a polymer or copolymer containing an olefin monomer as a main component. Paraffin wax is a petroleum-based wax composed of a mixture of chain-type saturated hydrocarbons having 20 to 30 carbon atoms. Sazole wax is a synthetic wax composed of substantially saturated linear hydrocarbons produced from carbon monoxide and hydrogen by the Fischer-Tropsch method.
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 suppressing the roller image of the pigment. Preferably, a wax emulsion containing a polyolefin wax is more preferable.

Examples of the olefin-based monomer used in the polyolefin-based 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 chain olefin as a main component are preferable, and those containing ethylene, propylene or butene as a main component are preferable. Specific examples thereof include polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, propylene-butene copolymer, ethylene-propylene-butene copolymer, ethylene-vinyl acetate copolymer and the like. Among these, polyolefin wax (polyethylene wax) containing ethylene as a main component is more preferable. Here, the main component occupies preferably 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 with respect to the entire components constituting the wax. To say.
The polyolefin-based wax is obtained by oxidizing the polyolefin-based wax by a known method, and is preferably used as the polyolefin-based wax because it can be easily emulsified in an aqueous solvent. The polyolefin-based oxide wax can be obtained by introducing an oxygen atom or the like into the molecule while adjusting the high-molecular-weight polyolefin-based resin to a desired molecular weight by thermal decomposition, chemical decomposition, or the like. Further, a modified wax such as glycol-modified polyethylene wax can also be used.
In the present invention, the polyolefin-based wax and the modified polyolefin-based wax are also included in the polyolefin-based 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 the polyolefin wax, the paraffin wax, and the sasol wax is preferably 65 parts by mass or more, more preferably 80 parts by mass or more, still more preferably 80 parts by mass or more, based on 100 parts by mass of the total wax. It is 90 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 100 parts by mass.

The method for obtaining the wax emulsion (D) is not particularly limited. For example, a method of emulsifying by mixing a polyolefin wax, another wax used as necessary, and a known surfactant can be mentioned. As the surfactant, a nonionic surfactant, an anionic surfactant and the like can be used.
Examples of the nonionic surfactant include ethylene oxide adducts of higher alcohols such as lauryl alcohol, cetyl alcohol, oleyl alcohol and stearyl alcohol, and ethylene oxide adducts of phenol alkylated with octyl group, nonyl group, dodecyl group and the like. .. Examples of the anionic surfactant include sulfate ester salts 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 a dodecyl group. Organophosphates can be mentioned.
Among these, an anionic wax emulsion obtained by emulsifying a wax with an anionic surfactant is more preferable from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink and suppressing the roller image of the pigment.
The pH of the wax emulsion (D) is 7 to 7 to higher in terms of further improving the storage stability and intermittent ejection stability of the ink, compatibility with other components in the ink, and suppressing metal corrosion in an inkjet nozzle or the like. It is preferably 12, and more preferably 8 to 11.
The pH can be measured by the method described in Examples.

The average particle size (average dispersion particle size) of the wax emulsion (D) in the ink further improves the dispersion stability of the wax emulsion, the storage stability of the ink, and the intermittent ejection stability, and suppresses the roller image of the pigment. From the viewpoint, it is preferably 800 nm or less, more preferably 500 nm or less, still more preferably 300 nm or less, still more preferably 100 nm or less, and preferably 10 nm or more, preferably 30 nm or more.
The average particle size (average dispersed particle size) of the wax emulsion can be measured by a dynamic light scattering method. For example, the average particle size (average dispersed particle size) is measured by the method described in Examples using a Microtrack particle size analyzer UPA manufactured by Nikkiso Co., Ltd. be able to.
Preferable examples of commercially available wax emulsions are AQUACER 507 manufactured by BIC Chemie, 513, 515, 526, 531 and 533, 537, 539, 552, 1547, and Chukyo Yushi Co., Ltd. Examples thereof include polyethylene wax emulsions such as Celozol 428, H620, 686, 524, Torasoru CN, Polylon L-787, L-788, and Chemipearl W900 and W4005 manufactured by Mitsui Chemicals, Inc.

<Surfactant (E)>
The water-based ink of the present invention preferably contains a surfactant (E) from the viewpoint of suppressing an increase in ink viscosity, further improving intermittent ejection stability, and suppressing roller image transfer of the pigment.
As the surfactant (E), a nonionic surfactant is preferable, and an acetylene glycol-based surfactant is more preferable, from the above viewpoint.
As the acetylene glycol-based surfactant, preferably 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 2, 5-Dimethyl-3-hexyne-2,5-diol, 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, 3,5-dimethyl-1-hexyne-3-ol, and One or more selected from these EO adducts, more preferably 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-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-. One or more selected from 5-decyne-4,7-diol and its EO adduct.

2,4,7,9-Tetramethyl-5-decine-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 desired acetylene glycol. For example, Takehiko Fujimoto, fully revised edition "Introduction to New Surfactants" (Sanyo Kasei). It can be obtained by the method described on pages 94 to 107 (published by Kogyo Co., Ltd., 1992).
As the acetylene glycol-based surfactant, a compound having an average addition molar number of ethylene oxide (hereinafter referred to as EO) of acetylene glycol of 5 or more and 35 or less is preferable from the viewpoint of suppressing an increase in ink viscosity.
The average number of moles of EO added to the acetylene glycol-based surfactant is more preferably 7 or more, further preferably 8 or more, still more preferably 9 or more, still more preferably 9.5 or more, and more preferably 30. Below, it is 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 of ethylene oxide in a desired number.
Commercially available products of the surfactant (E), particularly the acetylene glycol-based surfactant, include, for example, "Surfinol 465 (EO average number of moles added: 10, HLB) manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals. : 13) ”,“ Surfinol 485 (EO average number of moles added: 30, HLB: 17) ”,“ Acetylenol E81 (EO average number of moles added: 8.1, HLB: 12) ”manufactured by Kawaken Fine Chemicals Co., Ltd. , "Acetylenol E100 (EO average number of added moles: 10, HLB: 13)", "Acetylenol E200 (average number of added moles of EO: 20, HLB: 16)" and the like.

(Content of pigment (A))
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, still more preferably 2.5% by mass or more, from the viewpoint of improving the print density of the ink. Is. Further, from the viewpoint of lowering the ink viscosity at the time of solvent volatilization, further improving the intermittent ejection stability, and suppressing the roller image of the pigment, the ink is preferably 15.0% by mass or less, more preferably 10.0% by mass or less. It is more preferably 7.0% by mass or less, and even more preferably 5.0% by 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, 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, still more preferably 8.0% by mass or less. Below, it is more preferably 6.0% by mass or less.

(Content of polypropylene glycol (B))
The content of polypropylene glycol (B) in the ink is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further, from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink. It is preferably 0.8% by mass or more, and preferably 20% by mass or less, more preferably 16% by mass or less, still more preferably 12% by mass or less, still more preferably 10% by mass or less, still more preferably 8. It is mass% or less.

(Content of organic solvent (C))
The content of the organic solvent (C) in the ink is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, and more, from the viewpoint of further improving the intermittent ejection stability of the ink. It is 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, still more preferably 35% by mass or less.

(Content of wax emulsion (D))
The content of the wax emulsion (D) in the ink is preferably 0.1% by mass as the solid content in the ink from the viewpoint of the stability of the wax emulsion in the ink and the viewpoint of suppressing the roller image of the pigment. The above is more preferably 0.5% by mass or more, further preferably 1.0% by mass or more, still more preferably 2.0% by mass or more, and from the viewpoint of further improving the intermittent discharge stability, it is preferably 6% by mass. % Or less, more preferably 5% by mass or less, still more preferably 3% by mass or less.
The mass ratio [(B) / (D)] of polypropylene glycol (B) and wax emulsion (D) further improves the storage stability and intermittent ejection stability of the ink, and suppresses the roller image of the pigment. It is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and preferably 15 or less, more preferably 13 or less, still more preferably 11 or less.

(Content of surfactant (E))
The content of the surfactant (E) in the ink is preferably 0.1% by mass from the viewpoint of suppressing an increase in ink viscosity, further improving the intermittent ejection stability of the ink, and suppressing the roller image of the pigment. The above is more preferably 0.2% by mass or more, further 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 or less. Is.
(Water content)
The content of water in the ink is preferably 20% by mass or more, more preferably 30% by mass or more, and further, from the viewpoint of further improving the intermittent ejection stability and storage stability of the ink and suppressing the roller image of the pigment. It is 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, still more preferably 60% by mass or less.

(Other ingredients)
In addition to the above components, the ink of the present invention includes a moisturizing agent, a wetting agent, a penetrant, a dispersant, a surfactant other than an acetylene glycol-based surfactant, a viscosity modifier, a defoaming agent, and a preservative. , Various additives such as antifungal agents and anticorrosive agents can be added.

The water-based ink of the present invention is a mixture of pigment (A), polypropylene glycol (B), organic solvent (C), wax emulsion (D), water, and if necessary, other components such as surfactant (E). And can be obtained by stirring.

(Ink physical characteristics)
The viscosity of the ink at 32 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, still more preferably 5.0 mPa · s or more, from the viewpoint of further improving the intermittent ejection stability of the ink. It is s or more, preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, and further preferably 7.0 mPa · s or less.
The pH of the ink is preferably 7.0 or more, more preferably 8.0 or more, and further, from the viewpoint of further improving the storage stability and intermittent ejection stability of the ink and suppressing the roller image of the pigment. It is preferably 8.5 or more. From the viewpoint of member resistance and skin irritation, the pH is preferably 11.0 or less, more preferably 10.0 or less, and further preferably 9.5 or less.
The pH is measured by the method described in Examples.

[Inkjet printing method]
The inkjet printing method of the present invention is an inkjet printing method in which the water-based ink of the present invention is ejected from an ejection nozzle of an inkjet printing head onto a printing medium. The method of the inkjet printing head is a line head method, and the printing speed is high. The transfer speed of the print medium is 70 m / min or more, and the water absorption 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.
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 linked to this movement. An image or the like can be printed at high speed by ejecting ink droplets from the print medium and adhering the ink droplets to the printing medium.
Examples of the printing medium include a liquid-absorbent printing medium such as plain paper and high-quality paper, a low-liquid-absorbing printing medium such as art paper and coated paper, and a non-liquid-absorbing printing medium such as a synthetic resin film. The print medium is preferably roll paper.
Further, since the water-based ink of the present invention can maintain intermittent ejection stability even in high-speed printing, the printing speed is preferably 70 m / min or more, preferably 72 m / min or more, in terms of the transport speed of the printing medium. The transport speed of the print medium is the moving speed of the print medium in the moving direction. The printing speed is preferably 500 m / min or less, more preferably 300 m / min or less, still more preferably 150 m / min or less, from the viewpoint of drying the image or the like on the printed matter.
The water-based ink of the present invention has a roller image of a pigment even in a low-liquidity or non-liquid-absorbent printing medium in which the pigment tends to remain on the surface of the printing surface because the ink is absorbed slowly or is not absorbed. The print medium used in the method of the present invention has a water absorption amount of 0 g / m ² or more and 10 g / m ² or less, preferably 10 g / m ² or less, when the contact time between the print medium and pure water is 100 msec. It is 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.

The piezo method is preferable as the ink droplet ejection method, but a thermal method can also be adopted.
The applied voltage of the print head is preferably 5 V or more, more preferably 10 V or more, further 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 or the like. It is preferably 30 V or less.
The drive frequency is preferably 1 kHz or more, more preferably 5 kHz or more, further 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 and the like. It is as follows.
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 5 pL or less, more preferably 4.5 pL or less, still more preferably 4. It is 0 pL or less, more preferably 3.5 pL or less, and preferably 0.5 pL or more, more preferably 1.0 pL or more, still more preferably 1.5 pL or more, still more preferably 2 pL or more.
The print resolution is preferably 1200 dpi or more. For example, when the number of nozzle holes arranged in the line head per length of the nozzle row is 1200 dpi (dots / inch), when ink is ejected on the print medium, a corresponding row of 1200 dpi dots is formed. To. When the ink droplets are ejected while moving the print medium, dots are formed on the print medium along the direction of the nozzle row at a print resolution of 1200 dpi.

The temperature inside the ejection head, preferably inside the line head during printing, is preferably 20 ° C. or higher, more preferably 25 ° C. or higher, still more preferably 30 ° C. from the viewpoint of lowering the viscosity of the ink and further improving the intermittent ejection stability. ° C. or higher, preferably 45 ° C. or lower, more preferably 40 ° C. or lower, still more preferably 38 ° C. or lower.
The surface of the print medium facing the region where the ejection head, preferably the line head ejects ink, is preferably 28 ° C. or higher, more preferably 30 ° C. or higher, further preferably 31 ° C. or higher, and preferably 45 ° C. or lower. , More preferably 40 ° C. or lower, still more preferably 38 ° C. or lower.
The amount of ink adhered to the print medium is preferably 0.1 g / m ² or more, and preferably 25 g / m ² or less, more preferably 25 g / m ² or less as a solid content from the viewpoint of improving the image quality of the printed matter and the printing speed. It is 20 g / m ² or less, more preferably g / m ² or less.
In the inkjet printing method of the present invention, it is preferable to have a step of ejecting ink droplets onto a printing medium to print, and then drying the ink droplets that have landed on the printing medium.

With respect to the embodiments described above, the present invention further discloses the following water-based inks.
<1> A water-based ink containing a pigment (A), a polypropylene glycol (B), an organic solvent (C), a wax emulsion (D), and water, and the melting point of the wax contained in the wax emulsion (D) is 108 ° C. The above water-based ink.

<2> The water-based ink according to <1> above, wherein the pigment (A) is contained in the water-based ink as water-insoluble polymer particles containing the pigment.
<3> The aqueous solution according to <1> or <2> above, wherein the water-insoluble polymer is a vinyl-based polymer having (a) a structural unit derived from an ionic monomer and (b) a structural unit derived from a hydrophobic monomer. ink.
<4> The water-based ink according to <3> above, wherein the water-insoluble polymer further contains (c) a structural unit derived from a macromonomer.
<5> The water-based ink according to <3> or <4> above, wherein the water-insoluble polymer further contains (d) a structural unit derived from a nonionic monomer.
<6> (a) The content of the structural unit derived from the ionic monomer is preferably 5% by mass or more, more preferably 8% by mass or more, further preferably 10% by mass or more, and preferably 45% by mass or more. The water-based ink according to any one of <3> to <5> above, more preferably 35% by mass or less, still more preferably 30% by mass or less.
<7> (b) The content of the structural unit derived from the hydrophobic monomer is preferably 35% by mass or more, more preferably 40% by mass or more, further preferably 45% by mass or more, and preferably 90% by mass or more. The water-based ink according to any one of <3> to <6> above, more preferably 80% by mass or less, still more preferably 75% by mass or less.
<8> The weight average molecular weight of the water-insoluble polymer is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 20,000 or more, and preferably 500,000 or less, more preferably 400. The water-based ink according to any one of <2> to <7> above, which is 000 or less, more preferably 300,000 or less, still more preferably 200,000 or less.
<9> The mass ratio [(A) / (a)] of the pigment (A) to the water-insoluble polymer (a) in the pigment mixture is preferably 30/70 or more, more preferably 40/60 or more, still more preferably. The water-based ink according to any one of <2> to <8> above, which is 50/50 or more, preferably 90/10 or less, more preferably 80/20 or less, and further preferably 75/25 or less. ..

<10> Any of the above <2> to <9>, wherein the water-insoluble polymer particles containing the pigment (A) are produced as an aqueous dispersion by a method having the following steps I and II. The water-based ink described.
Step I: Dispersion treatment of a mixture containing a water-insoluble polymer, an organic solvent, a pigment (A), and water to obtain a dispersion of pigment-containing polymer particles Step II: The above from the dispersion obtained in Step I. Step of removing the organic solvent to obtain an aqueous dispersion of the pigment-containing polymer particles <11> The degree of polymerization of the polypropylene glycol (B) is preferably 3 or more, more preferably 4 or more, still more preferably 5 or more, still more. The water-based ink according to any one of <1> to <10> above, preferably 6 or more, and preferably 30 or less, preferably 25 or less, more preferably 20 or less, still more preferably 15 or less.
<12> The average molecular weight of polypropylene glycol (B) is preferably 250 or more, more preferably 300 or more, still more preferably 400 or more, even more preferably 500 or more, and preferably 2000 or less, more preferably 1800 or more. The water-based ink according to any one of <1> to <11> above, more preferably 1600 or less, still more preferably 1400 or less.
<13> The boiling point of the organic solvent (C) is preferably 150 ° C. or higher, more preferably 160 ° C. or higher, further preferably 180 ° C. or higher, and preferably 250 ° C. or lower, more preferably 246 ° C. or lower, further. The water-based ink according to any one of <1> to <12> above, preferably 215 ° C. or lower, more preferably 210 ° C. or lower, and even more preferably 200 ° C. or lower.
<14> The organic solvent (C) preferably contains one or more selected from diethylene glycol, propylene glycol and 2-pyrrolidone, and more preferably contains one or more selected from diethylene glycol and propylene glycol. > To <13>. The water-based ink according to any one of.

<15> The melting point of the wax contained in the wax emulsion (D) is preferably 110 ° C. or higher, more preferably 115 ° C. or higher, further preferably 120 ° C. or higher, and preferably 150 ° C. or lower, more preferably 145 ° C. or higher. The water-based ink according to any one of <1> to <14> above, which is below ° C., more preferably at least 140 ° C.
<16> The above-mentioned <1> to <15>, wherein the wax emulsion (D) preferably contains one or more selected from polyolefin wax and paraffin wax, and more preferably contains polyolefin wax. Water-based ink.
<17> The total content of one or more selected from polyolefin wax, paraffin wax, and sasol wax is preferably 65 parts by mass or more, more preferably 80 parts by mass or more, based on 100 parts by mass of the total amount of wax. The water-based ink according to any one of <1> to <16> above, more preferably 90 parts by mass or more, still more preferably 95 parts by mass or more, and even more preferably 100 parts by mass.
<18> The water-based ink according to any one of <1> to <17> above, wherein the pH of the wax emulsion (D) is preferably 7 to 12, more preferably 8 to 11.
<19> The average particle size (average dispersion particle size) of the wax emulsion (D) in the ink is preferably 800 nm or less, more preferably 500 nm or less, still more preferably 300 nm or less, still more preferably 100 nm or less. The water-based ink according to any one of <1> to <18>, which is preferably 10 nm or more, preferably 30 nm or more.
<20> The water-based ink according to <1> to <19> above, which further contains a surfactant (E).
<21> The water-based ink according to <20> above, wherein the surfactant (E) is preferably a nonionic surfactant, more preferably an acetylene glycol-based surfactant.

<22> 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, still more preferably 2.5% by mass or more, and preferably. Any of the above <1> to <21>, which is 15.0% by mass or less, more preferably 10.0% by mass or less, still more preferably 7.0% by mass or less, still more preferably 5.0% by mass or less. The water-based ink described in.
<23> 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. It is still more preferably 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, still more preferably 8. The water-based ink according to any one of <1> to <22> above, which is 0% by mass or less, more preferably 6.0% by mass or less.
<24> The content of polypropylene glycol (B) in the ink is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, still more preferably 0.8% by mass or more, and preferably. Is 20% by mass or less, more preferably 16% by mass or less, further preferably 12% by mass or less, still more preferably 10% by mass or less, still more preferably 8% by mass or less, the above <1> to <23>. The water-based ink described in any of.
<25> The content of the organic solvent (C) in the ink is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, still more preferably 25% by mass or more. The above-mentioned <1> to <24>, wherein the content is preferably 50% by mass or less, more preferably 45% by mass or less, further preferably 40% by mass or less, and even more preferably 35% by mass or less. Water-based ink.
<26> The content of the wax emulsion (D) in the ink is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and further preferably 1.0% by mass as the solid content in the ink. The above <1> to <25>, which are more preferably 2.0% by mass or more, preferably 6% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less. The water-based ink described in any of.
<27> The mass ratio [(B) / (D)] of polypropylene glycol (B) to wax emulsion (D) is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and preferably. The water-based ink according to any one of <1> to <26> above, wherein is 15 or less, more preferably 13 or less, still more preferably 11 or less.
<28> The content of the surfactant (E) in the ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and The water-based ink according to any one of <1> to <27> above, preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2.5% by mass or less.
<29> The content of water in the ink is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less. The water-based ink according to any one of <1> to <28> above, which is by mass or less, more preferably 75% by mass or less, still more preferably 60% by mass or less.

<30> An inkjet printing method for ejecting the water-based ink according to any one of claims 1 to 8 from an ejection nozzle of an inkjet printing head onto a printing medium.
The method of the inkjet printing head is the line head method,
The printing speed is 70 m / min or more in terms of the transport speed of the printing medium.
An inkjet printing method in which the water absorption 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.
<31> The above-mentioned <30>, wherein the printing speed is preferably 72 m / min or more, preferably 500 m / min or less, more preferably 300 m / min or less, and further preferably 150 m / min or less. Inkjet printing method.
<32> The inkjet printing method according to <30> or <31> above, wherein the water absorption of the print medium at a contact time of 100 msec between the print medium and pure water is preferably 5 g / m ² or less.
<33> The amount of ejected droplets of ink is preferably 5 pL or less per drop, more preferably 4.5 pL or less, still more preferably 4.0 pL or less, still more preferably 3.5 pL or less, and The inkjet printing method according to any one of <30> to <32> above, preferably 0.5 pL or more, more preferably 1.0 pL or more, still more preferably 1.5 pL or more, still more preferably 2 pL or more.

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

(1) Measurement of degree of polymerization of polypropylene glycol and calculation of average molecular weight The degree of polymerization was identified by using the following two methods using liquid chromatography.
(1-1) Calculation of composition ratio Polypropylene glycol was dissolved in a mixed solution of water and acetonitrile so as to be 0.1%, and the LC-CAD method (manufactured by Shimadzu Corporation, liquid chromatography device, column: L- The composition ratio was calculated by measuring with a Solution ODS C18 (4.6 × 250 mm, 5 μm), column temperature: 25 ° C., data injection amount: 20 μL, detector: CAD). At this time, the resolution of each composition ratio peak was improved by changing the ratio of the acetonitrile solution in the eluate.
(1-2) Identification of Degree of Polymerization of Each Composition Ratio Polypropylene glycol was dissolved in a mixed solution of water and acetonitrile so as to be 0.01%, and the LC-MS method [(Agile Technology Co., Ltd., liquid chromatography device) , Column: L-Polypropylene ODS C18 (4.6 × 250 mm, 5 μm), Column temperature: 25 ° C., Data injection volume: 20 μL, Ionization solution: 10 mM ammonium nitrate / methanol, Detector: ESI-MS), and each composition The degree of polymerization corresponding to the specific peak was determined.
(1-3) Calculation of average molecular weight The average molecular weight was calculated by applying the following formula from the abundance ratio of each degree of polymerization obtained by calculating the composition ratio and identifying the degree of polymerization of each composition ratio.
Average molecular weight = Σ {(degree of polymerization x 58) x abundance ratio of each degree of polymerization} / 100%

(2) Measurement of weight average molecular weight of water-insoluble polymer Gel permeation using a solution prepared by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively, as an eluent. A simple molecule whose molecular weight is known 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]. Measured using dispersed polystyrene.

(3) Measurement of average particle size of pigment-containing 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 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 volatiles, and left in a desiccator for another 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.

(5) Measurement of melting point of wax The melting point of wax was measured by a measuring device conforming to JIS K 0064. Specifically, a differential scanning calorimeter (Q20, manufactured by TA Instrument) was used to raise the temperature of the sample to 200 ° C., and then cool the sample to 0 ° C. at a temperature lowering rate of 10 ° C./min. Next, the temperature of the sample was raised at a heating rate of 10 ° C./min, and the amount of heat was measured up to 200 ° C. Among the observed heat of fusion peaks, the temperature of the peak having the largest peak area was defined as the maximum melting peak temperature, and the peak temperature was defined as the melting point.
(6) Measurement of Average Particle Size of Wax Emulsion The average particle size (average dispersed particle size) of the wax emulsion was measured using a Microtrack particle size analyzer UPA manufactured by Nikkiso Co., Ltd.

(7) Measurement of pH of water-based ink Water-based 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.
(8) Measurement of water absorption of the recording medium The water absorption of the recording medium at a contact time of 100 msec between the recording medium and pure water was determined by using an automatic scanning liquid absorption meter (KM500win, manufactured by Kumagai Riki Kogyo Co., Ltd.). Under the conditions of 23 ° C. and 50% relative humidity, the amount of transition of pure water at a 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 an 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" (Toa Synthetic Co., Ltd.) Made by the company, number average molecular weight 6,000, solid content 50%) 30 parts, polypropylene glycol methacrylate "Blemmer PP-1000" (Nichiyu Co., Ltd.) 25 parts, methyl ethyl ketone 25 parts are mixed to prepare 140 parts of monomer mixture. did.
In the reaction vessel, 18 parts of methyl ethyl ketone, 0.03 part of 2-mercaptoethanol as a chain transfer agent, and 10% (14 parts) of the monomer mixture were placed and mixed, and nitrogen gas replacement was sufficiently performed.
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". (Manufactured by Wako Pure Chemical Industries, Ltd.) Put a mixed solution of 3 parts into a dropping funnel, raise the temperature to 75 ° C while stirring the mixed solution in the reaction vessel under a nitrogen atmosphere, and mix the mixed solution in the dropping funnel. 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 to obtain a water-insoluble polymer (weight average molecular weight). : 60,000) solution was obtained. The solid content concentration of the water-insoluble polymer solution was 60% by mass.

(2) Production of an aqueous dispersion of pigment-containing polymer particles The water-insoluble polymer solution obtained in (1) above was dried under reduced pressure, and 37 parts of the water-insoluble polymer (1) was dissolved in 148 parts of methyl ethyl ketone. As a neutralizing agent, 12.5 parts of a 5N sodium hydroxide aqueous solution, 2 parts of 25% ammonia water, and 372 parts of ion-exchanged water were added to C.I. I. Pigment Blue 15: 3 (PB 15: 3, manufactured by Dainichiseika Kogyo Co., Ltd.) was added in 100 parts to obtain a pigment mixture. The degree of neutralization was 100 mol%. The pigment mixture was mixed using a disper blade at 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 water-insoluble 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). , Pore diameter: 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% by mass, and the average particle size of the pigment-containing polymer particles was 100 nm.

Example 1 (Manufacturing of water-based ink)
24 parts (3.5 parts of pigment, 1.3 parts of water-insoluble polymer (1)) of aqueous dispersion (solid content 20% by mass) of pigment-containing polymer particles obtained in Production Example 1, polypropylene glycol 700 (Wako Pure Chemical Industries, Ltd.) Kogyo Co., Ltd .: Average molecular weight 670) 5 parts, diethylene glycol 30 parts, acetylene glycol-based surfactant (product name: Surfinol 465, Air Products & Chemicals, 2,4,7,9-tetramethyl-5- 1.5 parts of ethylene oxide 10 mol addition of decine-4,7-diol, 3.3 parts of wax emulsion (product name: AQUACER507, manufactured by BYK, solid content 30%), and the total amount should be 100 parts. Ion-exchanged water was added to and mixed. The obtained mixed solution was filtered through a filter "Mini Sartorius Syringe Filter" (manufactured by Sartorius, pore size: 1.2 μm, material: cellulose acetate) to obtain an aqueous ink having a pH of 8.8.

Examples 2 to 13 and Comparative Examples 1 to 4 (manufacturing of water-based ink)
In Example 1, a water-based ink was obtained by performing the same operation as in Example 1 except that the polypropylene glycol, the wax emulsion and the solvent shown in Table 1 were used to obtain the compounding composition shown in Table 1. ..

[Polypropylene glycol: manufactured by Wako Pure Chemical Industries, Ltd.]
-PPG300: Polypropylene glycol 300 (triol type, average molecular weight 290)
PPG400: Polypropylene glycol 400 (diol type, average molecular weight 459)
-PPG700: Polypropylene glycol 700 (diol type, average molecular weight 670)
PPG1000: Polypropylene glycol 1000 (diol type, average molecular weight 1028)
-PPG1500: Polypropylene glycol 1500 (triol type, average molecular weight 1562)

[Organic solvent: manufactured by Wako Pure Chemical Industries, Ltd.]
-Diethylene glycol (boiling point 244 ° C)
-Propylene glycol (boiling point 188 ° C)
2-Pyrrolidone (boiling point 245 ° C)

[Wax emulsion]
AQUACER507 (anionic emulsion of high-density oxidized polyethylene wax, melting point 130 ° C., pH 9.7, average particle size 50 nm, manufactured by BYK)
AQUACER515 (high density polyethylene oxide emulsion, melting point 135 ° C., pH 9.5, average particle size 100 nm, manufactured by BYK)
-AQUACER537 (modified paraffin wax emulsion, melting point 110 ° C., pH 9.5, average particle size 61 nm, manufactured by BYK)
AQUACER1547 (anionic emulsion of high-density oxidized polyethylene wax, melting point 125 ° C., pH 9.7, average particle size 70 nm, manufactured by BYK)
Chemipearl W4005 (low molecular weight polyethylene wax emulsion, melting point 130 ° C., pH 11, average particle size 600 nm, manufactured by Mitsui Chemicals, Inc.)
-AQUACER526 (modified ethylene vinyl acetate wax emulsion, melting point 105 ° C., pH 9.7, manufactured by BYK)
Polylon L-787 (anionic emulsion of polyethylene wax, melting point 102 ° C., manufactured by Chukyo Yushi Co., Ltd.)

<Evaluation test of water-based ink>
(Preparation of inkjet printed matter)
Conducted on a WEB printing type printing evaluation device (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 water-based ink obtained in Examples and Comparative Examples was filled.
The line head applied voltage was set to 26 V, the amount of droplets to be ejected was 7 pL, the printing resolution was 600 dpi, the number of flushing before ejection was 200, the negative pressure was 4.0 kPa, and the roll paper transport speed (printing speed) was set to 75 m / min.
As a print medium for roll paper, a print medium (“UPM Finesse Gloss” (manufactured by UPM), water absorption of 3.1 g / m ² ) is set in the print evaluation machine, and a print command is transferred to the print evaluation device to be water-based. The ink was printed on a printing medium by an inkjet printing method. Immediately after the printing, a printed matter was prepared by passing it through a warm air dryer (set temperature 60 ° C.), and the following evaluation tests 1 to 3 were performed. The results are shown in Table 1.

Test 1 (storage stability)
The prepared ink was stored in a closed container at 70 ° C. in a constant temperature room. After one week, they were taken out, and the viscosity (E-type viscometer) and the particle size were measured to observe the changeability from the initial stage. The evaluation criteria are as follows.
(Evaluation criteria)
4: The change in viscosity after 1 week at 70 ° C. is less than 5%.
3: The change in viscosity after 1 week at 70 ° C. is 5% or more and less than 10%.
2: The change in viscosity after 1 week at 70 ° C. is 10% or more and less than 20%.
The viscosity change after 1 week at 1: 70 ° C. is 20% or more, or the ink loses fluidity and is not at a level at which the viscosity can be measured.

Test 2 (Intermittent discharge stability: Discharge recovery rate (%))
After preparing the inkjet printed matter, the printing press was stopped for 30 minutes and the printing line head was exposed to the atmosphere. After 30 minutes had passed, the ejection state of the first solid printed matter when printing was restarted was observed, the ejection recovery rate (%) was calculated by the following formula, and the intermittent ejection stability was evaluated.
Discharge recovery rate (%) = [(Discharge area for solid printing after 30 minutes exposure to the atmosphere / Discharge area for solid printing before test)] x 100
It is judged that the larger the discharge recovery rate (%) is, the better the intermittent discharge stability is, and if the numerical value is 70 or more, it can be put into practical use.

Test 3 (Suppression of pigment roller image: Transfer resistance (%))
Visually confirm the decrease in printing area before and after paper transfer using the stainless steel metal transfer roller installed on the print evaluation machine, calculate the transfer resistance (%) by the following formula, and obtain the pigment roller image. evaluated.
Transfer resistance (%) = (printed area after roller transfer / print area before roller transfer) x 100
It is judged that the larger the transfer resistance (%) is, the more the roller image can be suppressed, and if the numerical value is 80% or more, it can be practically used.

From Table 1, it can be seen that the inks of Examples 1 to 13 achieve storage stability, intermittent ejection stability, and pigment roller image suppression at a high level in a well-balanced manner as compared with the inks of Comparative Examples 1 to 4. ..

Claims (8)

Ejecting an aqueous ink to the print medium from the ejection nozzles of the ink jet print head, an inkjet printing method,
The water-based ink contains the pigment (A), polypropylene glycol (B), organic solvent (C), wax emulsion (D) and water, and the melting point of the wax contained in the wax emulsion (D) is 108 ° C. or higher. Is ink
The method of the inkjet printing head is the line head method,
The printing speed is 70 m / min or more in terms of the transport speed of the printing medium.
An inkjet printing method in which the water absorption 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. The inkjet printing method according to claim 1, wherein the content of polypropylene glycol (B) is 0.2% by mass or more and 20% by mass or less in the water-based ink. The inkjet printing method according to claim 1 or 2, wherein the polypropylene glycol (B) has an average molecular weight of 250 or more and 2000 or less. The inkjet printing method according to any one of claims 1 to 3, wherein the wax emulsion (D) is an anionic wax emulsion. The inkjet printing method according to any one of claims 1 to 4, wherein the content of the wax emulsion (D) is 0.1% by mass or more and 6% by mass or less as a solid content in the water-based ink. The inkjet printing method according to any one of claims 1 to 5, wherein the content of the organic solvent (C) is 10% by mass or more and 50% by mass or less in the water-based ink. The inkjet printing method according to any one of claims 1 to 6, wherein the mass ratio [(B) / (D)] of polypropylene glycol (B) to wax emulsion (D) is 1 or more and 15 or less. Pigment (A) is, as a water-insoluble polymer particles containing a pigment, Ru Tei is contained in the aqueous ink, an inkjet printing method according to any one of claims 1 to 7.