JP6806318B2 - Inkjet recording method - Google Patents

Description

The present invention relates to an inkjet recording method.

The inkjet recording method is a recording method in which ink droplets are directly ejected from a very fine nozzle onto a recording medium and adhered to obtain characters or images. This method is remarkably popular because it has many advantages that it is easy to make full color, it is inexpensive, plain paper can be used as a recording medium, and it does not contact the printed matter.
On the other hand, printing on a recording medium for commercial printing using a low water-absorbent coated paper such as offset coated paper or a film of a non-water-absorbent resin such as polyvinyl chloride resin, polypropylene resin, or polyester resin is required. It's coming.
When printing is performed on these low-water-absorbent and non-water-absorbent recording media by the inkjet recording method, the liquid components are slowly absorbed or not absorbed, so that it takes time to dry the ink and beading of a solid image (adjacent). It is known that the dots are attracted to each other and cause mottled unevenness in the image density).

In order to solve these problems, a liquid is formed by ejecting and adhering an ink containing a colorant after performing a pretreatment for previously adhering a component that agglomerates the colorant contained in the ink onto a recording medium. An inkjet recording method has been proposed with the aim of making it applicable to a recording medium in which absorption of components is slow.
For example, Patent Document 1 describes a pigment in which a pigment is dispersed by a reaction solution containing a polyvalent metal and at least an anionic polymer dispersant as an image forming method for obtaining a high-quality image having uniform scratch resistance. An image forming method using an aqueous ink containing a dispersion and having a specific absorbance when mixed with a reaction solution under specific conditions is disclosed.
Patent Document 2 describes a water-insoluble polymer obtained by copolymerizing a monomer mixture containing a styrene-based macromonomer as an image forming method capable of forming an image excellent in long-term ejection reliability, image gloss, scratch resistance, and the like. An image forming method using an ink set containing an ink composition containing a pigment coated with, a polymer particle, a water-soluble organic solvent, and water and a maintenance liquid is disclosed. Then, in the examples, it is disclosed that the reaction solution is applied to a recording medium with a wire coater and then printed with an ink composition.
In Patent Document 3, as an ink composition excellent in ultraviolet curability, scratch resistance, and drawing property, it is coated with a specific water-soluble polymerizable compound and a polymer having a crosslinked structure having an acid value of 25 to 150 mgKOH / g. An image forming method including an ink composition containing a pigment and a step of applying the ink composition to a recording medium and a step of applying a treatment liquid containing a coagulant for aggregating the components in the ink composition to the recording medium is disclosed. Has been done.

Japanese Unexamined Patent Publication No. 2005-298809 Japanese Unexamined Patent Publication No. 2011-38025 Japanese Unexamined Patent Publication No. 2011-178895

However, the techniques described in Patent Documents 1 to 3 are insufficient in scratch resistance as an inkjet recording method, although beading is suppressed to some extent, and from the viewpoint of achieving both beading suppression and scratch resistance. Further improvement of the ink composition is required.
An object of the present invention is to provide an inkjet recording method capable of both suppressing beading and scratch resistance when recording on a recording medium having low water absorption.

The present inventors attach a pretreatment liquid containing a flocculant that agglomerates components in an aqueous ink to a recording medium having low water absorption, and then apply a pigment to a portion of the recording medium to which the pretreatment liquid adheres. In an inkjet recording method for ejecting a water-based ink containing polymer particles containing, the polymer constituting the polymer particles contained in the water-based ink is crosslinked by a water-insoluble polymer and a water-insoluble polyfunctional epoxy compound, and the polymer is formed. It has been found that the above problems can be solved by appropriately adjusting the acid value, the degree of neutralization and the degree of cross-linking.
That is, the present invention is an inkjet recording method for recording on a recording medium having low water absorption using an aqueous ink containing crosslinked polymer particles containing a pigment.
The crosslinked polymer is obtained by cross-linking a water-insoluble polymer P having a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound, and the acid value of the water-insoluble polymer P is medium. The degree of sum and the degree of cross-linking satisfy the following condition 1,
Provided is an inkjet recording method having the following steps 1 and 2.
Step 1: Adhere the pretreatment liquid containing the flocculant that agglomerates the crosslinked polymer to the recording medium having low water absorption Step 2: Water-based ink on the portion of the recording medium obtained in Step 1 to which the pretreatment liquid adheres. Condition 1: [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) is -30 mgKOH / g or more and 130 mgKOH / It is less than or equal to g.
Here, the degree of neutralization is a percentage (mol%) of "molar equivalent of neutralizer / molar equivalent of carboxy group of water-insoluble polymer P", and the degree of cross-linking is "molar of epoxy group of water-insoluble polyfunctional epoxy compound". Equivalent number / molar equivalent number of carboxy groups of the water-insoluble polymer P "percentage (mol%).

According to the present invention, it is possible to provide an inkjet recording method capable of both suppressing beading and scratch resistance when recording on a recording medium having low water absorption.

[Inkjet recording method]
The inkjet recording method of the present invention is an inkjet recording method for recording on a recording medium having low water absorption using a water-based ink containing crosslinked polymer particles containing a pigment.
The crosslinked polymer is obtained by cross-linking a water-insoluble polymer P having a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound, and the acid value of the water-insoluble polymer P is medium. The degree of sum and the degree of cross-linking satisfy the following condition 1,
This is an inkjet recording method having the following steps 1 and 2.
Step 1: Adhere the pretreatment liquid containing the flocculant that agglomerates the crosslinked polymer to the recording medium having low water absorption Step 2: Water-based ink on the portion of the recording medium obtained in Step 1 to which the pretreatment liquid adheres. Condition 1: [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) is -30 mgKOH / g or more and 130 mgKOH / It is less than or equal to g.
Here, the degree of neutralization and the degree of cross-linking are as described above.
In addition, "water-based" means that water occupies the largest proportion in the medium in which the pigment is dispersed, and "low water absorption" is a concept including non-water absorption, and the recording medium and the recording medium. It means that the amount of water absorbed by the recording medium at a contact time of 100 msec with pure water is 10 g / m ² or less and 0 g / m ² or more.
Further, "recording" is a concept including printing and printing for recording characters and images, and "recorded matter" is a concept including printed matter and printed matter on which characters and images are recorded.

According to the inkjet recording method of the present invention, both beading suppression and scratch resistance can be achieved at the same time. The reason is not clear, but it can be considered as follows.
The inkjet recording method of the present invention contains a pigment contained in a water-based ink by adhering a pretreatment liquid to a recording medium having low water absorption and then ejecting the water-based ink to a portion to which the pretreatment liquid has adhered. The crosslinked polymer particles come into contact with the flocculant in the pretreatment liquid and aggregate. The crosslinked polymer constituting the crosslinked polymer particles containing the pigment is obtained by cross-linking the water-insoluble polymer P having a relatively high acid value with a water-insoluble polyfunctional epoxy compound, and the acid value and the degree of neutralization of the water-insoluble polymer P. By appropriately adjusting the degree of cross-linking, dissolution of the polymer in water and separation from the pigment are suppressed. Then, the rapid aggregation of the pigment is alleviated, and the liquid component in the water-based ink rapidly permeates and evaporates on the recording medium, whereby a strong film containing the pigment is formed on the recording medium, and the liquid component is released. The formation of a brittle coating containing is suppressed. Therefore, even if the recording medium has low water absorption, beading is suppressed by controlling the aggregation behavior described above, and a strong film is formed, so that it is considered that a recorded material having excellent scratch resistance can be obtained. ..
Hereinafter, the pigment, the crosslinked polymer, the water-based ink, and the pretreatment liquid used in the method of the present invention will be described first.

<Pigment>
The pigment used in the present invention is contained in the water-based ink as crosslinked polymer particles containing the pigment from the viewpoint of achieving both suppression of beading and scratch resistance.
Here, "containing a pigment" means a form in which a pigment is encapsulated in a crosslinked polymer having a crosslinked structure obtained by a reaction between a water-insoluble polymer P having a carboxy group and a water-insoluble polyfunctional epoxy compound. The polymer includes a form in which a part of the pigment is encapsulated and a part of the pigment is exposed from the crosslinked polymer, or a form in which the crosslinked polymer is attached to the surface of the pigment, and a mixture thereof is also included. .. Among these, a form in which a pigment is encapsulated in a crosslinked polymer is preferable.
The pigment contained in the crosslinked polymer particles is preferably a pigment from the viewpoint of imparting weather resistance and water resistance to the printed matter. That is, crosslinked polymer particles containing a pigment (hereinafter, also referred to as "pigment-containing polymer particles") are preferable.
The pigment is not particularly limited, and may be either an inorganic pigment or an organic pigment, and a rake pigment or a fluorescent pigment may be used. In addition, if necessary, they can be used in combination with extender pigments.

Specific examples of the inorganic pigment include carbon black, titanium oxide, alumina, iron oxide, red iron oxide, metal oxides such as chromium oxide, and pearl luster pigments. Especially for black ink, carbon black is preferable. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
These inorganic pigments may be those treated with a known hydrophobizing agent such as a titanium coupling agent, a silane coupling agent, or a higher fatty acid metal salt.
Specific examples of organic pigments include anthraquinone pigments, quinacridone pigments, indigo pigments, dioxazine pigments, perylene pigments, perinone pigments, isoindolinone pigments, isoindolin pigments, phthalocyanine pigments, and quinophthalone pigments. , One or more selected from condensed polycyclic pigments such as diketopyrrolopyrrole pigments, and azo pigments such as disazo pigments and condensed azo pigments. Among these, one or more selected from quinacridone pigments, azo pigments and phthalocyanine pigments is preferable from the viewpoint of color reproducibility of the obtained image.
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.

Specific examples of quinacridone pigments include C.I. I. Pigment Red (PR) 122, PR192, PR202, PR207, PR209, and C.I. I. Pigment Violet 19, etc., and one or more selected from PR122 and PV19 are more preferable.
Specific examples of the azo pigment include C.I. I. Pigment Yellow (PY) 74, PY151, PY154, PY155, PY180, PY213 and the like, and one or more selected from PY74 and PY154 are more preferable.
Specific examples of the phthalocyanine pigment include C.I. I. Pigment Blue (PB) 15: 1, PB15: 2, PB15: 3, PB15: 4, PB15: 5, PB15: 6, PB16, Pigment Green (PG) 7, PG36, etc., PB15: 3, And one or more selected from PB15: 4 are more preferable.
The organic pigment includes a derivative of the organic pigment which is a raw material. The pigment derivative can be prepared by subjecting a functional group such as a hydroxyl group, a carboxy group, a carbamoyl group, a sulfo group, a sulfonamide group, and a phthalimidemethyl group to the surface of an organic pigment.
Examples of the extender pigment include silica, calcium carbonate, talc and the like.
The above pigments can be used alone or in combination of two or more.

<Crosslinked polymer>
The crosslinked polymer used in the present invention is used to stably disperse the pigment in an aqueous medium and maintain the state.
The crosslinked polymer has a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less from the viewpoint of achieving both suppression of beading and scratch resistance (hereinafter, simply "water-insoluble polymer P"). ”) Is crosslinked with a water-insoluble polyfunctional epoxy compound. The crosslinked polymer is preferably neutralized with at least a part of the carboxy groups of the water-insoluble polymer P with a neutralizing agent, preferably an alkali metal compound, and then crosslinked with the water-insoluble polyfunctional epoxy compound in a state in which the pigment is dispersed. It is formed in an aqueous medium by reacting. In this case, the crosslinked polymer is not isolated, but the above condition 1 is determined by the monomer composition of the water-insoluble polymer P, the type and amount of the neutralizing agent (alkali metal compound), and the type and amount of the water-insoluble polyfunctional epoxy compound. , The state of the crosslinked polymer can be defined as satisfying the condition 1.

(Water-insoluble polymer P)
The water-insoluble polymer P for preparing the crosslinked polymer has a function as a dispersant for pigments and a function as a fixing agent for a recording medium.
This water-insoluble polymer P is water-insoluble not only in an unneutralized state but also after a part of its carboxy group is neutralized. Here, the "water-insoluble polymer" means that when the water-insoluble polymer is dispersed in water, it does not become transparent. Even if the aqueous dispersion of the water-insoluble polymer looks transparent visually, it is judged to be water-insoluble if the Tyndall phenomenon is observed by observation with laser light or normal light.

The acid value of the water-insoluble polymer P is derived from the carboxy group and is 200 mgKOH / g or more, preferably 210 mgKOH / g or more, and 320 mgKOH / g or less, preferably 300 mgKOH / g or less, more preferably 270 mgKOH or less. It is less than / g. When the acid value is in the above range, the amount of the carboxy group and its neutralized carboxy group is sufficient, and the dispersion stability of the pigment is ensured. It is also preferable from the viewpoint of the balance between the affinity between the crosslinked polymer and the aqueous medium and the interaction between the crosslinked polymer and the pigment.
The acid value of the water-insoluble polymer P can be calculated from the mass ratio of the constituent monomers. It can also be determined by a method of dissolving or swelling the polymer in a suitable organic solvent (for example, MEK) and titrating it.

The present form of the crosslinked polymer obtained by cross-linking the water-insoluble polymer P with a water-insoluble polyfunctional epoxy compound in the water-based ink includes (i) a state of being adsorbed on a pigment and (ii) a pigment. There are pigment-encapsulated (capsule) states and (iii) forms in which the pigment is not adsorbed. From the viewpoint of the dispersion stability of the pigment, the state of (i) or (ii) is preferable in the present invention, and (ii) the pigment-encapsulating state containing the pigment is more preferable.
Examples of the water-insoluble polymer P used include one or more selected from polyester, polyurethane, and vinyl-based polymers. From the viewpoint of improving the storage stability of water-based inks, vinyl compounds, vinylidene compounds, and vinylene compounds are used. A vinyl-based polymer obtained by addition polymerization of one or more selected vinyl monomers is preferable.

Examples of the water-insoluble polymer P include (a) a carboxy group-containing vinyl monomer (hereinafter, also referred to as “(a) component”) and (b) a hydrophobic vinyl monomer (hereinafter, also referred to as “(b) component”). A vinyl-based polymer obtained by copolymerizing a vinyl monomer mixture containing the mixture (hereinafter, also simply referred to as “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). This vinyl-based polymer is further derived from a structural unit derived from (c) macromonomer (hereinafter, also referred to as “(c) component”) and (d) nonionic monomer (hereinafter, also referred to as “(d) component”). Can contain building blocks.

[(A) Carboxylic group-containing vinyl monomer]
(A) The carboxy group-containing vinyl monomer is used as a monomer component of the water-insoluble polymer P from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based ink. As the carboxy group-containing vinyl monomer, a carboxylic acid monomer is used.
Examples of the carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid, and the like, and one selected from acrylic acid and methacrylic acid. The above is preferable.

[(B) Hydrophobic vinyl monomer]
(B) The hydrophobic vinyl monomer is used as a monomer component of the water-insoluble polymer P from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based ink. Examples of the hydrophobic vinyl monomer include an alkyl group having 1 to 22 carbon atoms, an alkyl (meth) acrylate having an aryl group having 6 to 22 carbon atoms, 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 propyl (meth). Acrylate, butyl (meth) acrylate, amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) Acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) acrylate, isoamyl (meth) acrylate, isooctyl (meth) acrylate, isodecyl (meth) acrylate, isododecyl (meth) acrylate, isostearyl (meth) ) Acrylate and the like can be mentioned.
In addition, "(meth) acrylate" means one or more kinds 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 heteroatom, is preferable, and a styrene-based monomer and an aromatic group-containing (meth) acrylate Is more preferable.
As the styrene-based monomer, styrene, α-methylstyrene, vinyltoluene, and divinylbenzene are preferable, and styrene and α-methylstyrene are more preferable.
Further, as the aromatic group-containing (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate and the like are preferable, and benzyl (meth) acrylate is more preferable.
(B) As the hydrophobic monomer, 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 water-insoluble from the viewpoint of improving the dispersion stability of pigment-containing polymer particles in an aqueous ink. It can be used as a monomer component of polymer P. 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 water-based ink. Is 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 Vinyl Monomer, and styrene and benzyl (meth) acrylate are preferable, and styrene. Is 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 P, (d) a nonionic monomer can be further used as a monomer component from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based ink.
(D) As the nonionic monomer, 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. Same) Polyalkylene glycol (meth) acrylate such as (meth) acrylate, polyethylene glycol (n = 2-30) (meth) acrylate, alkoxypolyalkylene glycol such as methoxypolyethylene glycol (n = 1-30) (meth) acrylate Examples thereof include (meth) acrylate, phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1 to 30, ethylene glycol: n = 1 to 29) (meth) acrylate and the like. Among these, polypropylene glycol (n = 2 to 30) (meth) acrylate and phenoxy (ethylene glycol / propylene glycol copolymer) (meth) acrylate are preferable, and polypropylene glycol (n = 2 to 30) (meth) acrylate is preferable. More preferred.

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.
As described above, the water-insoluble polymer P having a carboxy group used in the present invention includes a structural unit derived from one or more (a) carboxy group-containing vinyl monomers selected from acrylic acid and methacrylic acid, and an acrylate monomer and a methacrylate monomer. A vinyl polymer containing a structural unit derived from one or more (b) hydrophobic vinyl monomers selected from the aromatic group-containing monomers is preferable. Further, it may be a vinyl polymer further containing (c) a structural unit derived from a macromonomer and (d) a structural unit derived from a nonionic monomer.

(Content of each component or structural unit in the monomer mixture or polymer)
The content of (a) a carboxy group-containing vinyl monomer and (b) a hydrophobic vinyl monomer in a monomer mixture during the production of the water-insoluble polymer P (content as an unneutralized amount; the same applies hereinafter), that is, the water-insoluble polymer P. The content of the constituent units derived from each component in the mixture is as follows from the viewpoint of both the storage stability of the obtained water-based ink and the suppression of beading and the scratch resistance.
The content of the component (a) is preferably 20% by mass or more, more preferably 23% by mass or more, further preferably 25% by mass or more, and preferably 75% by mass or less, more preferably 60% by mass or less. , More preferably 55% by mass or less, still more preferably 50% by mass or less.
The content of the component (b) is preferably 15% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less. , More preferably 70% by mass or less.
When the component (c) is contained, the content of the component (c) is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 8% 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 0.3 or more, more preferably 0.32 or more, still more preferably 0.35 or more, and preferably 2.0 or less. It is more preferably 1.5 or less, still more preferably 1.2 or less.
When the component (c) is contained, the mass ratio of [(a) component / [(b) component + (c) component]] is preferably 0.1 or more, more preferably 0.3 or more, and further. It is preferably 0.5 or more, preferably 2.0 or less, more preferably 1.7 or less, still more preferably 1.5 or less.

(Manufacture of water-insoluble polymer P)
The water-insoluble polymer P is produced by copolymerizing the 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 particularly limited, but a polar organic solvent is preferable. When the polar organic solvent is miscible with water, it can be mixed with water and used. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 5 carbon atoms, ethers, and esters such as ethyl acetate. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water is preferable, and methyl ethyl ketone or a mixed solvent of it and water is preferable.
At the time of polymerization, a polymerization initiator or a polymerization chain transfer agent can be used.
Examples of the polymerization initiator include azo compounds such as 2,2'-azobisisobutyronitrile and 2,2'-azobis (2,4-dimethylvaleronitrile), t-butylperoxyoctate, benzoyl peroxide and the like. A known radical polymerization initiator such as the organic peroxide of the above can be used. The amount of the radical polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per 1 mol of the monomer mixture.
As the polymerization chain transfer agent, known chain transfer agents such as octyl mercaptan, mercaptans such as 2-mercaptoethanol, and thiuram disulfides can be used.
Further, the mode of chaining the polymerization monomers is not limited, and any polymerization mode such as random, block, and graft may be used.

Preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent and the like used, but usually the polymerization temperature is preferably 30 ° C. or higher, more preferably 50 ° C. or higher, and preferably 95 ° C. or lower. More than 80 ° C. The polymerization time is preferably 1 hour or more, more preferably 2 hours or more, and preferably 20 hours or less, more preferably 10 hours or less. 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. Further, the obtained polymer can be purified by removing unreacted monomers and the like 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, the solvent used in the polymerization reaction is not removed, and the contained organic solvent is used as the organic solvent used in step I described later, so that it is water-insoluble as it is. It is preferably used as a 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 number average molecular weight of the water-insoluble polymer P used in the present invention is preferably 2,000 or more, more preferably 5,000 or more, still more preferably 10,000, from the viewpoint of achieving both beading suppression and scratch resistance. The above, and preferably 20,000 or less, more preferably 18,000 or less. The weight average molecular weight is preferably 6,000 or more, more preferably 8,000 or more, and preferably 80,000 or less, more preferably 40,000 or less.
The number average molecular weight can be measured by the method described in Examples.

[Manufacture of pigment-containing polymer particles]
The water-insoluble polymer P particles containing a pigment (pigment-containing polymer particles) can be efficiently produced as an aqueous dispersion by a method having the following steps I to III.
Step I: A mixture containing a water-insoluble polymer P having a carboxy group, an organic solvent, a neutralizing agent, a pigment, and water (hereinafter, also referred to as “pigment mixture”) is dispersed and treated to disperse 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 III: Step A step of cross-linking the pigment aqueous dispersion obtained in II with a water-insoluble polyfunctional epoxy compound to obtain an aqueous pigment dispersion containing crosslinked polymer P particles containing a pigment.

(Step I)
Step I is a step of dispersing a water-insoluble polymer P having a carboxy group, an organic solvent, a neutralizing agent, a pigment, and a mixture containing water (pigment mixture) to obtain a dispersion of pigment-containing polymer particles. ..
The mixing order in step I is not particularly limited, but the water-insoluble polymer P is first dissolved in an organic solvent, and a neutralizing agent, water, a pigment, and if necessary, a surfactant and the like are added in this order to obtain the product. A method of adding and mixing with an organic solvent solution to obtain an oil-in-water dispersion is preferable.
The organic solvent used is not limited, but aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, esters and the like are preferable, and wettability to pigments, solubility of water-insoluble polymer P, and water-insoluble polymer P are preferable. From the viewpoint of improving the adsorptivity of the ester to the pigment, a ketone having 4 or more and 8 or less carbon atoms is more preferable, acetone, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is even more preferable.
When the water-insoluble polymer P is synthesized by the solution polymerization method, the solvent used in the polymerization may be used as it is.

(Neutralization)
At least a portion of the carboxy group of the water-insoluble polymer P is neutralized with a neutralizing agent, preferably an alkali metal compound. The pH of the obtained water-based pigment dispersion and water-based ink is preferably 5.5 or more, more preferably 6 or more from the viewpoint of handleability such as reducing skin irritation, and from the viewpoint of suppressing corrosion of members. 13 or less is preferable, 12 or less is more preferable, and 11 or less is further preferable.
Alkali metal compounds that are neutralizers are compounds that generate alkali metal ions in water-based media such as water and water-based inks, and are, for example, alkali metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide. Alkali metal salts of silicic acid such as hydroxide, sodium orthosilicate, sodium metasilicate, sodium sesquisilicate, alkali metal salt of phosphoric acid such as trisodium phosphate, carbonic acid such as disodium carbonate, sodium hydrogencarbonate, dipotassium carbonate, etc. Examples thereof include alkali metal salts of boric acid and alkali metal salts of boric acid such as sodium borate. Two or more kinds of alkali metal compounds may be combined. As the alkali metal compound, alkali metal hydroxide is preferable, and sodium hydroxide and potassium hydroxide are more preferable. Moreover, the water-insoluble polymer P 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 50% by mass or less, preferably 25% by mass or less. More preferred.

The degree of neutralization of the carboxy group of the water-insoluble polymer P is preferably 15 mol% or more, more preferably 20 mol%, from the viewpoint of achieving both storage stability of the obtained water-based ink, suppression of beading, and scratch resistance. Above, it is more preferably 25 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less, still more preferably 50 mol% or less.
Here, the degree of neutralization is a percentage (mol%) obtained by dividing the molar equivalent number of the neutralizing agent (alkali metal compound) by the molar equivalent number of the carboxy group of the water-insoluble polymer P, that is, "neutralizing agent (alkali metal compound)". ) Mole equivalent number / molar equivalent number of carboxy groups of the water-insoluble polymer P ”is a percentage (mol%). In the present invention, since the degree of neutralization is calculated from the molar equivalent number of the alkali metal compound, it exceeds 100 mol% when the alkali metal compound is excessively used.

Further, in step I, a volatile basic compound may be used in combination with the alkali metal compound. Examples of the volatile basic compound include ammonia, trimethylamine, triethylamine and the like, but ammonia is preferable from the viewpoint of high volatility.
The amount of the volatile basic compound used is not particularly limited, but if it is not used at all or is used, it is 10 mol% or more, preferably 20 mol% or more, more preferably 25 mol% or more, still more preferably 30 mol. % Or more, and preferably 100 mol% or less, more preferably 90 mol% or less, still more preferably 80 mol% or less, still more preferably 75 mol% or less. Only the amount of the alkali metal compound used is used for calculating the degree of neutralization, and the amount of the volatile basic compound used is not used for calculating the degree of neutralization of the present invention.

(Content of each component in pigment mixture)
The content of each component in the pigment mixture is as follows from the viewpoint of both the storage stability of the obtained water-based ink and the suppression of beading and the scratch resistance.
The content of the pigment in the pigment mixture in step I is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 12.5% by mass or more, and preferably 35% by mass or less. It is preferably 30% by mass or less, more preferably 20% by mass or less.
The content of the water-insoluble polymer P in the pigment mixture is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 3.0% by mass or more, and preferably 8. It is 0% by mass or less, more preferably 7.0% by mass or less, still more preferably 6.0% by mass or less.
The content of the organic solvent in the pigment mixture is preferably 4% by mass or more, more preferably 5% by mass or more, still more preferably 6% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or more. % Or less, more preferably 15% 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, further preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass. Hereinafter, it is more preferably 80% by mass or less.

The mass ratio of the pigment to the water-insoluble polymer P in the pigment mixture [pigment / water-insoluble polymer P] is preferably 0.5 or more, more preferably 1.0, from the viewpoint of the viscosity and storage stability of the obtained water-based ink. As mentioned above, it is more preferably 2.0 or more, and preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.5 or less.

(Dispersion treatment of pigment mixture)
The method for dispersing the pigment mixture in step I is not particularly limited. 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, and 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, but 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)
Step II is a step of removing the organic solvent from the dispersion obtained in Step I to obtain an aqueous dispersion of pigment-containing polymer particles (pigment aqueous dispersion). The removal of the organic solvent can be carried out by a known method.
From the viewpoint of suppressing the generation of aggregates in the process of removing the organic solvent and improving the dispersion stability of the aqueous pigment dispersion, water was added to the dispersion obtained in step I before removing the organic solvent. It is preferable to add it to adjust the mass ratio of the organic solvent to water (organic solvent / water).
The mass ratio of (organic solvent / water) is preferably 0.08 or more, more preferably 0.10 or more, and preferably 0.40 or less, more preferably 0.20 or less.

Examples of the organic solvent removing device used in the step II include a batch simple distillation device, a vacuum distillation device, a thin film distillation device such as a flash evaporator, a rotary distillation device, and a stirring type distillation device. From the viewpoint of efficiently removing the organic solvent, a rotary distillation apparatus and a stirring evaporator are preferable, and when removing an organic solvent from a small amount of dispersion-treated product of 5 kg or less at a time, a rotary distillation apparatus is preferable. When removing the organic solvent from a large amount of dispersion treated product exceeding 5 kg, a stirring type evaporator is preferable. Among the rotary distillation apparatus, a rotary vacuum distillation apparatus such as a rotary evaporator is preferable, and among the stirring type evaporators, a stirring tank thin film type evaporator and the like are preferable.
The temperature of the dispersion when removing the organic solvent can be appropriately selected depending on the type of the organic solvent used, but is preferably 20 ° C. or higher, more preferably 25 ° C. or higher, and preferably 80 ° C. or lower under reduced pressure. More preferably, it is 70 ° C. or lower.
The pressure at this time is preferably reduced pressure, and the absolute pressure is preferably 0.01 MPa or more, more preferably 0.02 MPa or more, and preferably 0.2 MPa or less, more preferably 0.1 MPa or less. is there.
The time for removing the organic solvent is preferably 30 minutes or more, more preferably 1 hour or more, and preferably 24 hours or less, more preferably 12 hours or less.
The removal of the organic solvent is preferably carried out until the solid content concentration is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less. It is preferable to do so.

The organic solvent is removed as described above, and the obtained concentrate is preferably subjected to a centrifugation treatment to recover the liquid layer portion. The recovered liquid layer portion is mainly an aqueous dispersion in which pigment-containing polymer particles are dispersed in water, and the solid layer portion is mainly a component composed of coarse particles generated due to poor dispersion or aggregation.
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.
In step II, the dispersion can also be heat-stirred before distilling off the organic solvent.
The obtained pigment aqueous dispersion is one in which pigment-containing polymer particles 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 at least the particles may be formed by the pigment and the water-insoluble polymer P. However, as described above, the particle form in which the pigment is contained in the water-insoluble polymer P. Is preferable.

The concentration of the non-volatile component (solid content concentration) of the obtained aqueous pigment dispersion is preferably 10% by mass or more from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion and facilitating the preparation of the aqueous ink. It is preferably 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 50 nm or more, more preferably 60 nm or more, still more preferably, from the viewpoint of reducing coarse particles and achieving both suppression of beading and scratch resistance. It is 70 nm or more, preferably 200 nm or less, more preferably 160 nm or less, and further preferably 130 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in Examples.

(Step III)
Step III is a step of cross-linking the pigment aqueous dispersion obtained in Step II with a water-insoluble polyfunctional epoxy compound to obtain an aqueous pigment dispersion containing cross-linked polymer P particles containing a pigment.
In step III, the pigment-containing polymer particles in the pigment aqueous dispersion obtained in step II were used from the viewpoint of achieving both storage stability of the obtained aqueous pigment dispersion and water-based ink, suppression of beading, and scratch resistance. A part of the carboxy group of the constituent water-insoluble polymer P is crosslinked to form a crosslinked structure on the surface layer of the pigment-containing polymer particles. In this way, the water-insoluble polymer P contained in the pigment-containing polymer particles in the pigment aqueous dispersion is crosslinked with the water-insoluble polyfunctional epoxy compound to produce a crosslinked polymer, and the pigment is dispersed with the crosslinked polymer to obtain an aqueous pigment dispersion. ..
The average particle size of the pigment-containing polymer particles in the water-based pigment dispersion is preferably 50 nm from the viewpoint of reducing coarse particles, storage stability of the water-based ink of the water-based ink, and both suppression of beading and scratch resistance. As described above, it is more preferably 60 nm or more, further preferably 70 nm or more, and preferably 200 nm or less, more preferably 170 nm or less, still more preferably 140 nm or less.
Further, the average particle size of the pigment-containing polymer particles in the water-based ink is the same as the average particle size in the water-based pigment dispersion, and the preferred average particle size is the preferred aspect of the average particle size in the pigment aqueous dispersion. Is the same as.

<Water-insoluble polyfunctional epoxy compound>
The water-insoluble polyfunctional epoxy compound (crosslinking agent) used in the present invention is dissolved in 100 g of water at 20 ° C. from the viewpoint of efficiently cross-linking with the carboxy group of the water-insoluble polymer P in a medium mainly composed of water. In addition, the dissolved amount is preferably 55 g or less, more preferably 44 g or less, still more preferably 39 g or less.
Further, the water-insoluble polyfunctional epoxy compound has a water content of preferably 50% by mass or less, more preferably 40% by mass, from the viewpoint of achieving both storage stability of the obtained water-based ink, suppression of beading and scratch resistance. % Or less, more preferably 35% by mass or less.
Here, the water content (mass%) means the dissolution rate (mass%) when 10 parts by mass of the epoxy compound is dissolved in 90 parts by mass of water at room temperature of 25 ° C., and more specifically, in Examples. Measured by the method described.

The water-insoluble polyfunctional epoxy compound is preferably a compound having two or more epoxy groups in the molecule, more preferably a compound having a glycidyl ether group, and further preferably a polyvalent compound having a hydrocarbon group having 3 or more and 8 or less carbon atoms. It is a glycidyl ether compound of alcohol.
The molecular weight of the water-insoluble polyfunctional epoxy compound is preferably 120 or more, more preferably 150 or more, still more preferably 200 or more, and from the viewpoint of ease of reaction and storage stability of the obtained crosslinked polymer. It is preferably 2000 or less, more preferably 1500 or less, and even more preferably 1000 or less.
The number of epoxy groups in the water-insoluble polyfunctional epoxy compound is 2 or more, preferably 3 or more per molecule, from the viewpoint of efficiently cross-linking with the carboxy group to improve the storage stability of the pigment-containing polymer particles. It is preferably 6 or less per molecule. Those having 5 or more epoxy groups in one molecule are poorly available on the market, and therefore, those having 3 or 4 epoxy groups in one molecule are more preferable from the viewpoint of achieving both reactivity and economy.
From the same viewpoint as above, the epoxy equivalent of the water-insoluble polyfunctional epoxy compound is preferably 100 or more, more preferably 110 or more, further preferably 120 or more, and preferably 300 or less, more preferably 270 or less. More preferably, it is 250 or less.

Specific examples of the water-insoluble polyfunctional epoxy compound include polypropylene glycol diglycidyl ether, glycerin polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, and pentaerythritol polyglycidyl. Examples thereof include polyglycidyl ethers such as ethers, resorcinol diglycidyl ethers, neopentyl glycol diglycidyl ethers, and hydrogenated bisphenol A type diglycidyl ethers.
Among these, one or more selected from polypropylene glycol diglycidyl ether (water content 31%), trimethylolpropane polyglycidyl ether (water content 27%), and pentaerythritol polyglycidyl ether (water content less than 20%) are preferable. ..

(Crosslink reaction)
In the present invention, a part of the carboxy group of the water-insoluble polymer P is neutralized with a neutralizing agent, preferably an alkali metal compound, the pigment is dispersed, and then a part of the carboxy group of the water-insoluble polymer P is further added. It is preferable to form a crosslinked structure by reacting with a water-insoluble polyfunctional epoxy compound to obtain an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium with a crosslinked polymer obtained in the system. At that time, from the viewpoint of achieving both storage stability of the obtained water-based ink, suppression of beading, and scratch resistance, a neutralizing agent (alkali metal compound) and a water-insoluble polyfunctional epoxy are used in an amount satisfying the following condition 1. Use a compound.

[Condition 1]
Condition 1 is that the value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage (mol%) of "molar equivalent number of neutralizer (alkali metal compound) / molar equivalent number of carboxy group of water-insoluble polymer P", and the degree of cross-linking is "water-insoluble polyfunctional epoxy compound". The molar equivalent of the epoxy group / the molar equivalent of the carboxy group of the water-insoluble polymer P ”is a percentage (mol%).
Condition 1 indicates the amount of unneutralized carboxy groups of the water-insoluble polymer P in the water-based ink required to suppress beading and enhance the storage stability, and the acid value and neutralization degree of the water-insoluble polymer P. , Determined by the degree of cross-linking. In other words, Condition 1 represents the acid value of the water-insoluble polymer P after neutralization and cross-linking.
If the value of Condition 1 is -30 mgKOH / g or more and 130 mgKOH / g or less, the amount of charge on the pigment surface is sufficient when a pigment dispersion is prepared using the polymer, and the water-insoluble polymer P, and thus the crosslinked polymer. The water insolubility of the polymer is also sufficient, and it is possible to achieve both suppression of beading and scratch resistance at a high level.
The value of condition 1 is preferably -20 mgKOH / g or more, more preferably -10 mgKOH / g or more, still more preferably -5 mgKOH / g or more, even more preferably 30 mgKOH / g or more, and preferably 120 mgKOH / g or more. Below, it is more preferably 100 mgKOH / g or less, still more preferably 80 mgKOH / g or less.
Since it is difficult to actually measure the amount of the water-insoluble polyfunctional epoxy compound that reacts with the carboxy group of the water-insoluble polymer P, the number of moles of the epoxy group of the water-insoluble polyfunctional epoxy compound used. Is converted into the acid value per 1 g of the water-insoluble polymer P used to disperse the pigment.

The temperature of the cross-linking reaction is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, still more preferably 55 ° C. or higher, still more preferably 60 ° C. or higher, still more preferably 65 ° C. The above, and preferably 95 ° C. or lower, more preferably 90 ° C. or lower.
From the same viewpoint as above, the reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, still more preferably 1.5 hours or more, still more preferably 3.0 hours or more. Then, it is preferably 12 hours or less, more preferably 10 hours or less, still more preferably 8.0 hours or less, still more preferably 6 hours or less.
The degree of cross-linking of the water-insoluble polymer P is preferably 5 mol% or more, more preferably 10 mol% or more, further preferably 15 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less. , More preferably 60 mol% or less. The degree of cross-linking is an apparent degree of cross-linking calculated from the acid value of the polymer and the equivalent of the epoxy group of the cross-linking agent. That is, the degree of cross-linking is a percentage (mol%) of "molar equivalent number of epoxy groups of water-insoluble polyfunctional epoxy compound / molar equivalent number of carboxy groups of water-insoluble polymer P".

The pH of the obtained aqueous pigment dispersion is preferably 8.0 or higher. When the pH is 8.0 or more, the dissociation of the anionic group is promoted, the amount of charge of the aqueous pigment dispersion is sufficient, and the storage stability of the aqueous pigment dispersion can be enhanced. The pH of the aqueous pigment dispersion is preferably 8.5 or more, and the upper limit thereof is not particularly limited. However, when the pH exceeds 11, the pH of the ink using the aqueous pigment dispersion becomes too high, and the ink is used. It is not preferable because it adversely affects the members of the printer or printing machine used. Therefore, the pH of the aqueous pigment dispersion is more preferably 10.5 or less.
The pH measuring method is not particularly limited, but a pH measuring method using a glass electrode is defined in JIS Z8802, and this method is preferable from the viewpoint of simplicity and accuracy.

<Water-based ink>
The water-based ink used in the present invention is prepared by producing an aqueous dispersion of water-insoluble polymer P particles (pigment-containing polymer particles) containing a pigment by the above steps I to III, and then an organic solvent or the like usually used for the water-based ink is used. It can be obtained by blending.
Further, if necessary, various additives such as wetting agent, penetrant, dispersant, surfactant, viscosity modifier, defoaming agent, preservative, fungicide, rust preventive, etc. are added, and further a filter is added. It can be obtained by performing a filtration treatment such as.

(Organic solvent)
The organic solvent is used from the viewpoint of further improving the storage stability of the water-based ink. The organic solvent used preferably contains one kind or two or more kinds of organic solvents having a boiling point of 90 ° C. or higher, and an organic solvent having a weighted average value of boiling points of 250 ° C. or lower is preferable. The weighted average value of the boiling points of the organic solvent is preferably 150 ° C. or higher, more preferably 180 ° C. or higher, and preferably 240 ° C. or lower, more preferably 220 ° C. or lower, still more preferably 200 ° C. or lower.
Examples of the organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds and the like. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferable, and one or more selected from ethylene glycol, propylene glycol, diethylene glycol, and triethylene glycol are more preferable, and propylene glycol and triethylene glycol are more preferable. One or more selected from the above is more preferable.

(Wetting agent)
The wetting agent is added for the purpose of preventing the ink from drying. For example, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, trihydric or higher alcohols such as glycerin, trimethylolpropane, and pentaerythritol, and glycerin ethylene glycol. Polyhydric alcohol alkyl ethers such as monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, polyhydric alcohol aryl ethers, including Examples thereof include nitrogen heterocyclic compounds, amides, amines and sulfur-containing compounds.

(Surfactant)
Surfactants are used to adjust ink properties such as surface tension. Examples of the surfactant include anionic, nonionic, cationic and amphoteric surfactants, and nonionic surfactants are preferable.
Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and glycerin fatty acid ester. , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkylalkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, Examples thereof include polyethylene glycol polypropylene glycol block copolymer.
As other surfactants, silicone-based surfactants such as polysiloxane oxyethylene adducts, fluorine-based surfactants, and the like can also be used.

The content and physical characteristics of each component of the water-based ink used in the present invention are as follows.
(Pigment content)
The content of the pigment in the water-based 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 print density and storage stability. And, preferably 15.0% by mass or less, more preferably 10.0% by mass or less, still more preferably 7.0% by mass or less.
(Content of crosslinked polymer)
The content of the crosslinked polymer in the water-based ink is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5 from the viewpoint of improving the scratch resistance of the printed matter printed on the low water absorption recording medium. It is preferably 12% by mass or less, more preferably 10% by mass or less, still more preferably 10% by mass or less, from the viewpoint of reducing the ink viscosity at the time of solvent volatilization and achieving both beading suppression and scratch resistance. It is 8% by mass or less.

(Content of pigment-containing polymer particles)
The content of the pigment-containing polymer particles in the water-based ink is preferably 1 from the viewpoint of accelerating the drying property on the paper surface when printed on a recording medium having low water absorption, and achieving both suppression of beading and scratch resistance. It is preferably 5% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and from the viewpoint of lowering the ink viscosity at the time of solvent volatilization and achieving both beading suppression and scratch resistance. It is 25% by mass or less, more preferably 20% by mass or less, still more preferably 15% by mass or less.
(Water content)
As the water used for the water-based ink of the present invention, pure water such as ion-exchanged water and distilled water and ultrapure water are preferable. The water content is preferably 45% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass in the water-based ink from the viewpoint of reducing the amount of the organic solvent used and improving the storage stability. % Or more, and preferably 85% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less.

(Water-based ink physical characteristics)
The viscosity of the water-based ink at 32 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, still more preferably 5.0 mPa · s, from the viewpoint of further improving the storage stability of the ink. It is s or more, and 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 water-based ink is preferably 7.0 or more, more preferably 7.2 or more, still more preferably 7.5 or more, from the viewpoint of further improving the storage stability of the ink. Further, 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.

<Pretreatment liquid>
The pretreatment liquid preferably does not contain a pigment, and contains one or more coagulants capable of forming agglomerates when in contact with the water-based ink.
The coagulant comes into contact with the water-based ink on a recording medium having low water absorption, so that the pigment-containing polymer particles stably dispersed in the water-based ink come into contact with the coagulant in the pretreatment liquid, and the pigment-containing polymer It promotes the aggregation of particles and exhibits a viscosity increasing effect.
The surface tension (25 ° C.) of the pretreatment liquid is preferably 10 mN / m or more, more preferably 15 mN / m or more, and preferably 45 mN / m, from the viewpoint of achieving both beading suppression and scratch resistance. Below, it is more preferably 40 mN / m or less.
The flocculant used in the present invention is preferably one or more selected from a cationic polymer, an organic acid or a salt thereof, and a polyvalent metal salt from the viewpoint of suppressing beading, and is cationic from the viewpoint of scratch resistance. One or more selected from the polymer and the polyvalent metal salt is more preferable, and the cationic polymer is further preferable.
The content of the flocculant is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, based on the total amount of the pretreatment liquid, from the viewpoint of suppressing beading. It is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less.

(Cationic polymer)
As the cationic polymer, a polymer having a cationic group such as a primary to tertiary amino group, a quaternary ammonium group, or hydrazine is preferable, and the cationic polymer is a homopolymer of a monomer having a cationic group or another. It is preferably a copolymer or a reduced polymer with a monomer.
The "cationic" of a cationic polymer means that when an unneutralized polymer is dispersed or dissolved in pure water, the pH becomes higher than 7, and in the case of a polymer having a quaternary ammonium group, the pH is paired. When the ions are dispersed or dissolved in pure water as hydroxide ions, the pH becomes higher than 7, or if the polymer or the like is insoluble in pure water and the pH cannot be clearly measured, the pH is changed to pure water. It means that the zeta potential of the dispersed dispersion becomes positive.
When a cationic polymer is used, the pH (25 ° C.) of the pretreatment liquid is preferably 5 or more, more preferably 6 or more, and preferably 8 or less, more preferably 8 or less, from the viewpoint of the aggregation rate of the water-based ink. It is 7 or less.
When a cationic polymer is used, in the present invention, from the viewpoint of achieving both beading suppression and scratch resistance, the pH (25 ° C.) of the water-based ink is 7.5 or more, and the pH of the pretreatment liquid (25). ° C.) is preferably 5 or more and 7 or less.
The cationic polymer is preferably a water-soluble polymer. Here, the "water-soluble polymer" refers to a polymer in which the amount of the polymer dissolved exceeds 10 g when the polymer is dried at 105 ° C. for 2 hours and the polymer reached a constant amount is dissolved in 100 g of water at 25 ° C. The dissolved amount thereof is preferably 20 g or more, more preferably 100 g or more.

Among the above cationic polymers, a cationic polymer having an amino group or a quaternary ammonium base is preferable from the viewpoint of achieving both suppression of beading and scratch resistance and improvement of storage stability of the pretreatment liquid. ..
Preferred examples of cationic polymers, polyethyleneimine, polyallylamine or an acid neutralization thereof, polydiallyl dimethyl ammonium chloride, diallyl dimethyl ammonium chloride -SO ₂ copolymer, dimethylaminoethyl methacrylate polymer or in their acid Examples thereof include one or more selected from Japanese products, polymethacryloyloxyethyltrimethylammonium chloride, and amine-epichlorohydrin copolymers, but more preferably amine-epichlorohydrin copolymers. These can be used alone or in combination of two or more.

The weight average molecular weight of the cationic polymer is preferably 1,000 or more, more preferably 3,000 or more, still more preferably 4,000 or more, from the viewpoint of suppressing beading due to good aggregation with the pigment-containing polymer particles. Yes, and preferably 300,000 or less, more preferably 100,000 or less, still more preferably 40,000 or less.
The content of the cationic polymer is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 10% by mass or more, based on the total amount of the pretreatment liquid, from the viewpoint of achieving both suppression of beading and scratch resistance. It is 15% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less.

(Organic acid and its salt)
The organic acid and its salt can form aggregates by changing the pH of the water-based ink. At this time, the pH (25 ° C.) of the pretreatment liquid is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and preferably 6 or less, from the viewpoint of the aggregation rate of the water-based ink. It is preferably 5 or less. When the pretreatment liquid contains an organic acid or a salt thereof, the pH (25 ° C.) of the water-based ink is preferably 7.5 or more, more preferably 8 or more.
When an organic acid and a salt thereof are used, in the present invention, the pH of the water-based ink (25 ° C.) is 7.5 or more, and the pH of the pretreatment liquid is from the viewpoint of achieving both suppression of beading and scratch resistance. (25 ° C.) is preferably 1 or more and 5 or less.

Examples of the organic acid include one or more selected from organic acids having a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfo group, a sulfinic acid group, a carboxy group, and salts thereof. Among these, from the viewpoint of achieving both suppression of beading and scratch resistance, an organic acid having a phosphate group or a carboxy group is preferable, and an organic acid having a carboxy group is more preferable. Among the organic acids having a carboxy group, an organic acid having a hydroxy group having 2 or more and 4 or less carbon atoms is preferable, and one or more selected from a dicarboxylic acid and a hydroxycarboxylic acid is more preferable, and the organic acid having 3 carbon atoms is more preferable. Alternatively, one or more selected from a dicarboxylic acid having 4 or a hydroxycarboxylic acid having 3 or 4 carbon atoms is more preferable.
Organic acids having a carboxy group include polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, sulfonic acid, and ortholine. Examples thereof include one or more selected from acids, pyrrolidone carboxylic acids, pyron carboxylic acids, pyrrol carboxylic acids, furan carboxylic acids, pyridine carboxylic acids, coumarin acids, thiophene carboxylic acids, nicotinic acids, derivatives thereof, and salts thereof. Among these, one or more selected from malonic acid, malic acid, glycolic acid, and salts thereof is preferable, and malonic acid is more preferable.
The content of the organic acid is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 12% by mass, based on the total amount of the pretreatment liquid, from the viewpoint of achieving both suppression of beading and scratch resistance. % Or more, and preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less.

(Multivalent metal salt)
Examples of polyvalent metal salts include alkaline earth metals of Group 2 of the periodic table such as magnesium and calcium, transition metals of Group 3 of the periodic table such as yttrium and lanthanoid, and alkaline earth metals of Group 8 of the periodic table such as iron. , Zinc and other metals of Group 12 of the Periodic Table, and salts of Metals of Group 13 of the Periodic Table such as aluminum. Among these, from the viewpoint of achieving both suppression of beading and scratch resistance, alkaline earth metal salts of Group 2 of the periodic table are preferable, magnesium salts and calcium salts are more preferable, and magnesium salts are even more preferable.
Examples of the counter ion of the metal ion include chloride ion, bromide ion, iodide ion, chlorate ion, perchlorate ion, bromine ion, nitrate ion, sulfate ion and the like, but when used as a salt, From the viewpoint of increasing water solubility, chloride ion and nitrate ion are preferable, and nitrate ion is most preferable.
That is, as the polyvalent metal salt, one or more selected from magnesium nitrate, calcium nitrate, magnesium chloride, and calcium chloride is preferable, and magnesium nitrate is more preferable.

When a polyvalent metal salt is used, the pH (25 ° C.) of the pretreatment liquid is preferably 5 or more, more preferably 6 or more, and preferably 8 or less, more preferably, from the viewpoint of the aggregation rate of the water-based ink. Is 7 or less.
When a polyvalent metal salt is used, in the present invention, from the viewpoint of achieving both beading suppression and scratch resistance, the pH (25 ° C.) of the water-based ink is 7.5 or more, and the pH of the pretreatment liquid (pretreatment liquid) ( 25 ° C.) is preferably 5 or more and 7 or less.
The content of the polyvalent metal salt is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 5% by mass or more, based on the total amount of the pretreatment liquid, from the viewpoint of achieving both suppression of beading and scratch resistance. It is 8% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less.

The pretreatment liquid includes organic solvents such as wetting agents and penetrants usually used for water-based inks for inkjet recording, surfactants such as dispersants and defoamers, viscosity modifiers, preservatives, fungicides, and rust preventives. Agents and the like may be added.
As the pretreatment liquid, for example, one or more selected from a cationic polymer, an organic acid or a salt thereof, and a polyvalent metal salt are added to water stirred by a stirring blade, and further, the additive, an organic solvent, and a surfactant are added. It can be obtained by adding an activator, water and the like and mixing.
The content of the organic solvent in the pretreatment liquid is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 15% by mass or more, from the viewpoint of coatability on the recording medium and affinity with the water-based ink. Is 40% by mass or less, more preferably 35% by mass or less.
The content of the surfactant in the pretreatment liquid is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, from the viewpoint of coatability on the recording medium and affinity with the water-based ink. Yes, and preferably 5% by mass or less, more preferably 3% by mass or less.
The content of water in the pretreatment liquid is preferably 40% by mass or more, more preferably 45% by mass or more, and preferably 45% by mass or more, from the viewpoint of coatability on a recording medium and affinity with water-based ink. It is 85% by mass or less, more preferably 80% by mass or less.

<Inkjet recording method>
The inkjet recording method of the present invention is an inkjet recording method for recording on a recording medium having low water absorption using an aqueous ink containing crosslinked polymer particles containing a pigment, and has the following steps 1 and 2.
Step 1: A pretreatment liquid containing a flocculant that agglomerates the crosslinked polymer is attached to a recording medium having low water absorption. Is discharged by the inkjet recording method to obtain a recorded material.

(Step 1)
Step 1 is a step of adhering a pretreatment liquid containing a flocculant that agglomerates the crosslinked polymer to a recording medium having low water absorption.
Details of the crosslinked polymer, flocculant and pretreatment solution are as described above.
By performing step 1 before step 2, it is possible to achieve both suppression of beading and scratch resistance. In this case, the time from adhering the pretreatment liquid to the recording medium until the water-based ink is ejected to the recording medium is not particularly limited, but from the viewpoint of suppressing bleeding and beading, the pretreatment liquid in step 1 It is preferable to have a drying step after adhering the ink to the recording medium and before ejecting the water-based ink to the recording medium in the step 2.

Examples of the recording medium include coated paper and film having low water absorption.
As coated paper, general-purpose glossy paper "OK Top Coat Plus" (manufactured by Oji Paper Co., Ltd., basis weight 104.7 g / m ² , water absorption amount at contact time 100 msec (the following water absorption amount is the same) 4.9 g / m ^2), multicolored foam gloss paper (manufactured by Oji paper Co., Ltd., basis weight 104.7 g / ^{m 2,} the water absorption amount ^{5.2g / m 2), UPM Finesse} gloss (UPM Co., basis weight 115 g / ^{m 2,} water Amount 3.1 g / m ² ), UPM Finesse Matt (UPM, basis weight 115 g / m ² , water absorption 4.4 g / m ² ), TerraPress Silk (Stora Enso, basis weight 80 g / m ² , water absorption The amount is 4.1 g / m ² ) and the like.
Examples of the film include polyester film, vinyl chloride film, polypropylene film, polyethylene film, nylon film and the like. These films may be subjected to surface treatment such as corona treatment, if necessary.
Examples of the film include Lumirer T60 (manufactured by Toray Industries, Inc., polyethylene terephthalate, water absorption 2.3 g / m ² ), PVC80BP (manufactured by Lintec Corporation, vinyl chloride, water absorption 1.4 g / m ² ) and the like.
The amount of water absorbed by the recording medium used in the present invention for a contact time of 100 msec with pure water is 10 g / m ² or less and 0 g / m ² or more. The water absorption amount is measured by the method described in Examples.

Examples of the method of adhering the pretreatment liquid to the recording medium having low water absorption in step 1 include known methods such as a coating method, a dipping method, and an inkjet method. As the coating method and dipping method, roll coater, gravure coater, die coater, curtain coater, spray coater, blade coater, wire bar coater, rod coater, impregnation coater, cast coater, air knife coater, reverse coater, lip coater, kiss coater. Etc. can be mentioned.
When applying the inkjet method, it is preferable to use a piezo type inkjet printer.
When the inkjet method is adopted, the surface tension (25 ° C.) of the pretreatment liquid is preferably 15 mN / m or more, more preferably 18 mN / m or more, from the viewpoint of achieving both beading suppression and scratch resistance. Then, it is preferably 50 mN / m or less, more preferably 45 mN / m or less, and further preferably 40 mN / m or less. The viscosity (20 ° C.) of the pretreatment liquid is preferably 1.0 mPa · s or more, more preferably 1.2 mPa · s or more, and preferably 12 mPa · s or less, more preferably 10 mPa · s or less. ..
The surface tension can be measured by the method described in Examples.

The amount of Wet adhering to the recording medium of the pretreatment liquid is not particularly limited as long as the water-based ink can be aggregated, but is preferably 0.5 g / m ² or more from the viewpoint of the aggregation rate and avoiding adverse effects on the surface of the recording medium. , More preferably 1 g / m ² or more, still more preferably 2 g / m ² or more, and preferably 10 g / m ² or less, more preferably 7 g / m ² or less, still more preferably 5 g / m ² or less. ..
The Wet adhesion amount means the adhesion amount per unit area before the pretreatment liquid solvent (for example, water) dries and volatilizes, and the solid content of the pretreatment liquid is added to the adhesion amount per unit area after drying. It means a quantity expressed as a numerical value multiplied by a ratio.
Examples of the heating method in the heating step after adhering the pretreatment liquid to the recording medium include a method of applying heat with a heater or the like from the side opposite to the adhesion surface of the pretreatment liquid of the recording medium, and adhesion of the pretreatment liquid of the recording medium. Examples thereof include a method of applying warm air or hot air to the surface, a heating method using an infrared heater, and the like, and a plurality of these may be combined and heated.

(Step 2)
The step 2 is a step of ejecting a water-based ink to a portion of the recording medium obtained in the step 1 to which the pretreatment liquid adheres by an inkjet recording method to obtain a recorded material.
In the inkjet recording method of the present invention, a known inkjet recording device can be used to eject water-based ink onto a recording medium to print and record an image.
Examples of the inkjet recording device include a continuous injection type (charge control type, spray type, etc.), an on-demand type (piezo method, thermal method, electrostatic suction method, etc.), and are used as a piezo type water-based ink for inkjet recording. Is more preferable.

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

(1) Measurement of number average molecular weight of water-insoluble polymer P N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography) and phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) And lithium bromide (manufactured by Tokyo Kasei Kogyo Co., Ltd., reagent) dissolved at a concentration of 60 mmol / L and 50 mmol / L, respectively, as an eluent, and a gel chromatography method [GPC apparatus manufactured by Toso Co., Ltd. (HLC- 8120 GPC), a column manufactured by Toso Co., Ltd. (TSK-GEL, α-M × 2), flow velocity: 1 mL / min], and a monodisperse polystyrene having a known molecular weight was used as a standard substance.

(2) Measurement of average particle size of pigment-containing polymer particles Cumulant analysis was performed using a laser particle analysis system "ELSZ-1000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25 ° C., an angle between the incident light and the detector of 165 °, and the number of integrations was 100 times, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. It was diluted with water so that the measured concentration was 5 × 10-3% by mass (converted to solid content concentration).

(3) Measurement of solid content concentration of pigment dispersion In a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), 10.0 g of sodium sulfate homogenized in a desiccator was weighed, and about 1.0 g of a sample was placed therein. Was added, mixed, weighed accurately, maintained at 105 ° C. for 2 hours to remove volatiles, and left in a desiccator for an additional 15 minutes to measure 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.

(4) Measurement of water content of epoxy compound 90 parts by mass of ion-exchanged water and 10 parts by mass of cross-linking agent were added to a glass tube (25 mmφ × 250 mmh) at room temperature of 25 ° C., and the glass tube was adjusted to a constant temperature of 25 ° C. It was allowed to stand in the tank for 1 hour. Then, the glass tube was vigorously shaken for 1 minute and then allowed to stand again in a constant temperature bath for 10 minutes. Then, the undissolved material was weighed and the water content (mass%) was calculated.

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

(9) Measurement of surface tension of pretreatment liquid Pick the platinum plate attached to the automatic surface tension meter "CBVP-Z" manufactured by Kyowa Surface Chemical Co., Ltd. installed in a constant temperature room at 25 ° C with tweezers, rinse with water, and use an alcohol lamp. After reddening with the oxidative flame of, attach it to the hook of the surface tension meter. The treatment liquid whose temperature has been adjusted to 25 ° C. is placed in a sample dish, placed on a stage, and the measurement is performed by pressing the measurement button. The measured value was the average value of the same sample measured three times.

<Preparation of water-insoluble polymer P>
Preparation Example A1
74 parts of methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., reagent), 66 parts of benzyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd., reagent), styrene macromer (manufactured by Toa Synthetic Co., Ltd., trade name: AS-6S, number average Molecular weight: 6000, solid content concentration 50%) 40 parts (20 parts as solid content), polypropylene glycol monomethacrylate (manufactured by Nichiyu Co., Ltd., trade name: Blemmer PP-800, average number of moles of propylene oxide added 13, terminal: hydroxyl group ) 40 parts were mixed to prepare a monomer mixed solution. In the reaction vessel, 20 parts of methyl ethyl ketone (MEK), 0.3 part of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixed solution were put and mixed, and nitrogen gas substitution was sufficiently performed.
On the other hand, in the dropping funnel, the remaining 90% of the monomer mixed solution, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK, and an azo radical polymerization initiator (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65). , 2,2'-azobis (2,4-dimethylvaleronitrile)) 2.2 parts of the mixed solution was added, and the temperature was raised to 65 ° C. while stirring the monomer mixed solution in the reaction vessel under a nitrogen atmosphere. The mixed solution in the dropping funnel was dropped over 3 hours. After 2 hours have passed at 65 ° C. from the end of the dropping, a solution prepared by dissolving 0.3 part of the polymerization initiator in 5 parts of MEK is added, and the mixture is further aged at 65 ° C. for 2 hours and 70 ° C. for 2 hours, and then the solid content concentration. MEK was added so that the concentration was 40.8% to obtain a water-insoluble polymer solution (i) having a carboxy group (number average molecular weight of polymer: 12000, acid value 240 mgKOH / g). The results are shown in Table 1.

Preparation Example A2
Acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 39 parts, styrene (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 151 parts, α-methylstyrene (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 9 parts are mixed. A monomer mixture was prepared. In the reaction vessel, 20 parts of MEK, 0.3 part of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were placed and mixed, and nitrogen gas replacement was sufficiently performed.
On the other hand, the remaining 90% of the monomer mixed solution, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK and 2.2 parts of the azo radical polymerization initiator (V-65) were put into the dropping funnel. After that, a water-insoluble polymer solution (ii) having a carboxy group having a solid content concentration of 40.8% was obtained in the same manner as in Preparation Example A1. The results are shown in Table 1.

Preparation Examples A3 to A5
In Preparation Example 2, water-insoluble polymer solutions (iii) to (v) having a carboxy group were obtained in the same manner as in Preparation Example A2 except that the amounts of acrylic acid and styrene were set to the amounts shown in Table 1. The results are shown in Table 1.

<Manufacturing of aqueous pigment dispersion of pigment-containing polymer particles>
Production Example 1 (Production of water-based pigment dispersion A1)
(1) Step I
158 g of the water-insoluble polymer solution (i) (solid content concentration 40.8%) obtained in Preparation Example 1 was mixed with 60.7 g of methyl ethyl ketone (MEK) and charged into a 2 L volume disper under the condition of 1400 rpm. While stirring, 446.9 g of ion-exchanged water and 20.9 g of a 5N sodium hydroxide aqueous solution (neutralization degree with sodium hydroxide 32%) were added, and the mixture was stirred at 1400 rpm for 15 minutes while cooling in a water bath at 0 ° C. Next, 256 g of a cyan pigment (CI Pigment Blue 15: 3, copper phthalocyanine, manufactured by DIC Corporation, trade name: TGR-SD) was added, and the mixture was stirred at 7000 rpm for 3 hours. Further, 1044 g of ion-exchanged water was added, and the obtained pigment mixture was subjected to 20-pass dispersion treatment at a pressure of 150 MPa using a microfluidizer "M-110EH-30XP" (manufactured by Microfluidics), and water was further added to solidify. A dispersion was obtained in which the concentration was adjusted to 21% by mass.
(2) Process II
1000 g of the dispersion obtained in step I was placed in a 2 L eggplant flask, 400 g of ion-exchanged water was added (solid content concentration 15.0% by mass), and a rotary distillation apparatus (manufactured by Tokyo Rika Kikai Co., Ltd., product name: rotary evaporator) was added. Using N-1000S), the organic solvent was removed by holding at a pressure of 0.09 MPa for 3 hours in a warm bath adjusted to 32 ° C. at a rotation speed of 50 rpm. Further, the warm bath was adjusted to 62 ° C., the pressure was lowered to 0.07 MPa, and the mixture was concentrated to a solid content concentration of 25.0% by mass.
The obtained concentrate was put into a 500 ml angle rotor, centrifuged at 7000 rpm for 20 minutes using a high-speed cooling centrifuge (manufactured by Hitachi Koki Co., Ltd., product name: himacCR22G, set temperature 20 ° C.), and then the liquid layer portion. Was filtered through a 5 μm membrane filter (manufactured by Sartorius, trade name: Minisart) to obtain a pigment aqueous dispersion a1 (solid content concentration 22.0% by mass).
(3) Process III
Proxel LVS (manufactured by Arch Chemicals Japan Co., Ltd., antifungal agent) was added to 400 g of the aqueous pigment dispersion a1 obtained in Step II, which was centrifuged and the supernatant was filtered to adjust the solid content concentration to 22.0% by mass. Effective content 20%) 0.89 g, water-insoluble polyfunctional epoxy compound (trimethylolpropane polyglycidyl ether, manufactured by Nagase ChemteX Corporation, trade name: Denacol EX321, water content 27%) so that the cross-linking rate is 40 mol%. , Epoxy equivalent 140) 4.2 g was added, and the mixture was stirred at 70 ° C. for 2 hours. After cooling to 25 ° C., the mixture is filtered through the 5 μm filter, ion-exchanged water is added so that the solid content concentration becomes 22.0% by mass, and an aqueous pigment dispersion of pigment-containing polymer particles (crosslinking degree 40 mol%) is added. I got A1. The results are shown in Table 2.

Production Example 2 (Production of water-based pigment dispersion A2)
(1) Step I
Except for using the polymer solution (ii) obtained in Preparation Example 2 (solid content concentration 40.8%) to make 13.1 g of a 5N sodium hydroxide aqueous solution (neutralization degree with sodium hydroxide 32%). A dispersion (solid content concentration 21.0% by mass) was obtained in the same manner as in Step I of Production Example 1.
(2) Process II
The pigment aqueous dispersion a2 (solid content concentration 22.0% by mass) was obtained in the same manner as in Step II of Production Example 1.
(3) Process III
Pigment-containing polymer particles in the same manner as in Step III of Production Example 1 except that 2.6 g of the water-insoluble polyfunctional epoxy compound (Denacol EX321) was added using the pigment aqueous dispersion a2 obtained in Step II. An aqueous pigment dispersion A2 (solid content concentration 22.0% by mass) having a degree of cross-linking of 40 mol% was obtained. The results are shown in Table 2.

Production Example 3 (Production of water-based pigment dispersion A3)
(1) Step I
Except for using the polymer solution (iii) (solid content concentration 40.8%) obtained in Preparation Example 3 to make 18.7 g of a 5N sodium hydroxide aqueous solution (neutralization degree with sodium hydroxide 32%). A dispersion (solid content concentration 21.0% by mass) was obtained in the same manner as in Step I of Production Example 1.
(2) Process II
The pigment aqueous dispersion a3 (solid content concentration 22.0% by mass) was obtained in the same manner as in Step II of Production Example 1.
(3) Process III
Pigment-containing polymer particles in the same manner as in Step III of Production Example 1 except that 3.8 g of the water-insoluble polyfunctional epoxy compound (Denacol EX321) was added using the pigment aqueous dispersion a3 obtained in Step II. Water-based pigment dispersion A3 was obtained. The results are shown in Table 2.

Production Examples 4 to 12 (Production of water-based pigment dispersions A4 to A12)
Using the polymer solution (iv) (solid content concentration 40.8%) obtained in Preparation Example 4, the amount of the 5N sodium hydroxide aqueous solution of Step I and the water-insoluble polyfunctional epoxy compound of Step III in Production Example 3 were used. Water-based pigment dispersions A4 to A12 of the pigment-containing polymer particles were obtained in the same manner as in Production Example 3 except that the amounts of the above were as shown in Table 2.

Production Example 13 (Production of water-based pigment dispersion A13)
Steps I to II were carried out in the same manner as in Steps I to II of Production Example 4 to obtain an aqueous pigment dispersion a4 (solid content concentration 22.0% by mass).
In step III, the pigment dispersion a4 obtained in step II was used to prepare a water-soluble polyfunctional epoxy compound (polyglycerol polyglycidyl ether, manufactured by Nagase ChemteX Corporation, trade name: Denacol EX521, epoxy equivalent 183). An aqueous pigment dispersion A13 of pigment-containing polymer particles was obtained in the same manner as in Step III of Production Example 1 except that 5 g was added. The results are shown in Table 2.

Production Example 14 (Production of water-based pigment dispersion A14)
(1) Step I
Except that the polymer solution (v) (solid content concentration 40.8%) obtained in Preparation Example 5 was used to make 32.3 g of a 5N sodium hydroxide aqueous solution (neutralization degree with sodium hydroxide 32%). A dispersion (solid content concentration 21.0% by mass) was obtained in the same manner as in Step I of Production Example 1.
(2) Process II
The pigment aqueous dispersion a10 was obtained in the same manner as in Step II of Production Example 1.
(3) Process III
Pigment-containing polymer particles in the same manner as in Step III of Production Example 1 except that 6.5 g of the water-insoluble polyfunctional epoxy compound (Denacol EX321) was added using the pigment aqueous dispersion a10 obtained in Step II. An aqueous pigment dispersion A14 (solid content concentration 22.0% by mass) having a degree of cross-linking of 40 mol% was obtained. The results are shown in Table 2.

Preparation Example B1 (Preparation of water-based ink 1)
Water-based pigment dispersion A1 (pigment concentration 5%), glycerin (manufactured by Kao Co., Ltd., concentrated glycerin for cosmetics, wetting agent) 5%, triethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd., reagent) obtained in Production Example 1. , Wetting agent) 7%, acetylenol E100 (manufactured by Kawaken Fine Chemicals Co., Ltd., nonionic surfactant, 10 mol of ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol) Add 0.5% and ion-exchanged water, weigh to 100% total amount, stir with a magnetic stirrer and mix well, 1.2 μm filter (acetylcellulose film, outer diameter: 2.5 cm). , Fujifilm Co., Ltd.) was attached and filtered through a 25 mL volume needleless reagent to obtain water-based ink 1.

Preparation Examples B2 to B19 (Preparation of water-based inks 2 to 19)
Water-based inks 2 to 19 were obtained in the same manner as in Preparation Example B1 except that the water-based pigment dispersion A1 used in Preparation Example B1 was changed to the water-based pigment dispersion shown in Table 3.

Preparation Example C1 (Preparation of amine-epichlorohydrin copolymer)
95.1 g of water and 131.8 g (0.8 mol) of 58% trimethylamine hydrochloride aqueous solution were charged into a 500 ml four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction tube, and nitrogen gas was introduced. 74.0 g (0.8 mol) of epichlorohydrin was added dropwise over 3 hours while cooling below so as not to exceed 40 ° C. After completion of the dropping, the temperature was raised to 80 ° C. and the reaction was carried out over 1 hour. Then, the mixture was cooled to 30 ° C., 36.1 g (0.4 mol) of a 50% aqueous dimethylamine solution and 14.8 g (0.2 mol) of calcium hydroxide were added, the temperature was raised to 80 ° C., and the reaction was carried out over 1 hour. I let you. Then, the reaction solution was adjusted to pH 4.0 and solid content concentration 50% with hydrochloric acid and water to obtain an amine-epichlorohydrin copolymer.

Preparation Examples D1 to D3 (Preparation of pretreatment solutions 1 to 3)
Polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm (Durapore SVLPO 4700, manufactured by Yamato Scientific Co., Ltd.) after mixing each component of the pretreatment solution with the composition shown below and stirring for 1 hour to uniformly mix them. ) Was filtered under pressure to remove coarse particles and dust to obtain pretreatment liquids 1 to 3.
The surface tension (25 ° C.) of the pretreatment liquid 1 was 20.6 mN / m, and the pH was 6.4.
The surface tension (25 ° C.) of the pretreatment liquid 2 was 37.3 mN / m, and the pH was 1.6.
The surface tension (25 ° C.) of the pretreatment liquid 3 was 31.5 mN / m, and the pH was 6.5.

(Composition of pretreatment liquid 1)
-Amine-epichlorohydrin copolymer obtained in Preparation Example C1: 20.0%
-3-Methyl-1,3-butanediol: 10.0%
・ Glycerin: 20%
2-Ethyl-1,3-hexanediol: 1.0%
-2,4,7,9-Tetramethyldecane-4,7-diol: 0.1%
-Fluorine-based surfactant (C ₄ F _9- CH ₂ CH (OH) CH ₂ O- (CH ₂ CH ₂ O) _25- C ₁₂ H ₂₅ ): 0.2%
-Proxel GXL (manufactured by Abyssia Co., Ltd., preservative): 0.05%
・ 1,2,3-benzotriazole: 0.05%
・ Ion-exchanged water: 48.6%

(Composition of pretreatment liquid 2)
・ Malonic acid (divalent carboxylic acid, manufactured by Wako Pure Chemical Industries, Ltd.): 15.0%
-Diethylene glycol monomethyl ether (manufactured by Wako Pure Chemical Industries, Ltd.): 20.0%
-Surfactant (N-ole oil-N-methyl taurine sodium): 1.0%
・ Ion-exchanged water: 64.0%

(Composition of pretreatment liquid 3)
-Magnesium nitrate hexahydrate (polyvalent metal salt) (reagent manufactured by Wako Pure Chemical Industries, Ltd.): 10%
・ Glycerin: 5%
・ Diethylene glycol: 5%
・ Isopropyl alcohol: 5%
・ Acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.): 0.2%
・ Ion-exchanged water: 74.8%

Example 1
(Step 1)
The pretreatment liquid 1 obtained in Preparation Example D1 was coated with a desktop coater (manufactured by Mitsui Denki Seiki Co., Ltd., trade name: TC-1) using coated paper (manufactured by Oji Paper Co., Ltd., trade name: OK Top Coat Plus). , A water absorption amount of 4.9 g / m ² ) at a contact time of 100 msec was applied so as to have a Wet adhesion amount of 0.8 g / m ^2, and dried at 23 ° C. for 24 hours to obtain precoated paper 1.
(Step 2)
A commercially available inkjet printer (manufactured by Ricoh Co., Ltd., GX-5500, piezo method) is filled with an aqueous ink 1 containing the aqueous pigment dispersion A1 obtained in Preparation Example B1 and precoated paper at 23 ° C. and 50% relative humidity. A4 solid image (single color) is printed on No. 1, and immediately after printing, it is heated and dried on an analog hot plate (NINOS) NA-2 (manufactured by AS ONE Co., Ltd.) heated to 80 ° C., and then 23. A printed matter was obtained by storing overnight at ° C. and a relative humidity of 50%.

Examples 2-3
A printed matter was obtained in the same manner as in Example 1 except that the pretreatment liquid and the water-based ink shown in Table 3 were used.
Examples 4-5
Coated paper (manufactured by Oji Paper Co., Ltd., OK top) using a wire bar coater (manufactured by Tester Sangyo Co., Ltd., trade name: ROD No. 2) with the pretreatment liquid 1 or 2 obtained in Preparation Example 1 or 2. Apply on Coat Plus) so that the amount of Wet adhered is 4.0 g / m ^2, and immediately after application, use "HOT PLATE HI-1000" manufactured by AS ONE to dry at 50 ° C for 2 seconds to apply pre-coated paper 2. Obtained.
Then, a printed matter was obtained in the same manner as in Step 2 of Example 1 except that the aqueous pigment dispersion A4 was used.

Examples 6-11
In Example 1, a printed matter was obtained in the same manner as in Example 1 except that the water-based ink 1 obtained in Preparation Example B1 was changed to the water-based inks 6 to 11 obtained in Preparation Examples B6 to B11.

Example 12
The pretreatment liquid 1 obtained in Preparation Example D1 was used on a PET film (manufactured by Toray Industries, Inc., Lumirror T60, contact time of 100 msec) using a desktop coater (manufactured by Mitsui Denki Seiki Co., Ltd., trade name: TC-1). It was applied onto a water absorption amount of 2.3 g / m ² ) so as to have a Wet adhesion amount of 0.8 g / m ^2, and dried at 23 ° C. for 24 hours to obtain a precoated paper. Then, a printed matter was obtained in the same manner as in Step 2 of Example 1 except that the aqueous pigment dispersion A4 was used.

Comparative Example 1
In Example 3, a printed matter was obtained in the same manner as in Example 3 except that the coated paper (OK Top Coat Plus) which had not been pretreated in Step 1 was used.

Comparative Example 2
The pretreatment liquid 1 obtained in Preparation Example 1 was placed on coated paper (Oji Paper Co., Ltd., OK Top Coat Plus) using a desktop coater (Mitsui Denki Seiki Co., Ltd., trade name: TC-1). The coating was applied so that the wet adhesion amount was 0.8 g / m ^2, and dried at 23 ° C. for 24 hours to obtain precoated paper 1. Then, a printed matter was obtained in the same manner as in Step 2 of Example 1 except that the aqueous pigment dispersion A2 was used.

Comparative Examples 3 to 6
A printed matter was obtained in the same manner as in Comparative Example 2 except that the water-based ink containing the water-based pigment dispersion shown in Table 3 was used.

Comparative Example 7
In Example 12, a printed matter was obtained in the same manner as in Example 12 except that the PET film (Lumilar T60) that had not been pretreated in Step 1 was used.

<Evaluation of printed matter 1-19>
The obtained printed matter was evaluated for scratch resistance and beading by the following methods. The results are shown in Table 3.

[Evaluation of scratch resistance]
The obtained printed matter was used 5 times (5 times) using a clock meter (manufactured by Imoto Seisakusho Co., Ltd., product name: QC-621A) and coated paper (manufactured by Oji Paper Co., Ltd., OK Top Coat Plus) as a friction material. A scratch test was performed on the printed matter by rubbing (reciprocating).
The print density of the ink transferred to the coated paper after the test was measured by an optical spectrophotometer (Sakata Inks Engineering Co., Ltd., trade name: SpectroEye). The results are shown in Table 3. The smaller the transfer density, the less ink is transferred and the better the scratch resistance.

[Evaluation of beading]
With respect to the obtained printed matter, the number of beading present in the field of view was visually counted using a digital microscope (Handy type image evaluation system, PIAS-II (Low resolution module) manufactured by Trek Japan Co., Ltd.). The results are shown in Table 3.
The smaller the number of beads, the better the performance. If it is 0 or 1, it is practically optimal, and if it is 4 or less, it can be put into practical use.

From Table 3, the inkjet recording methods of Examples 1 to 12 of the present invention have scratch resistance while suppressing beading when printed on a recording medium having low water absorption as compared with the inkjet recording methods of Comparative Examples 1 to 7. It turns out that it is excellent in sex.

Claims (7)

An inkjet recording method for recording on a recording medium having low water absorption using a water-based ink containing crosslinked polymer particles containing a pigment.
The crosslinked polymer is obtained by cross-linking a water-insoluble polymer P having a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound, and the acid value of the water-insoluble polymer P is medium. The degree of sum and the degree of cross-linking satisfy the following condition 1,
An inkjet recording method comprising the following steps 1 and 2.
Step 1: Adhere the pretreatment liquid containing the flocculant that agglomerates the crosslinked polymer to the recording medium having low water absorption Step 2: Water-based ink on the portion of the recording medium obtained in Step 1 to which the pretreatment liquid adheres. Condition 1: [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) is -30 mgKOH / g or more and 130 mgKOH / It is less than or equal to g.
Here, the degree of neutralization is a percentage (mol%) of "molar equivalent of neutralizer / molar equivalent of carboxy group of water-insoluble polymer P", and the degree of cross-linking is "molar of epoxy group of water-insoluble polyfunctional epoxy compound". Equivalent number / molar equivalent number of carboxy groups of the water-insoluble polymer P "percentage (mol%). The inkjet recording method according to claim 1, wherein the flocculant is one or more selected from a cationic polymer, an organic acid or a salt thereof, and a polyvalent metal salt. The inkjet recording method according to claim 2, wherein the cationic polymer is an amine-epichlorohydrin copolymer. The inkjet recording method according to claim 2, wherein the organic acid is an organic acid which may have a hydroxy group having 2 or more and 4 or less carbon atoms. The inkjet recording method according to claim 2, wherein the polyvalent metal salt is an alkaline earth metal salt of Group 2 of the periodic table. The inkjet recording method according to any one of claims 1 to 5, wherein the water-insoluble polymer P has a number average molecular weight of 2,000 or more and 20,000 or less. The inkjet recording method according to any one of claims 1 to 6, wherein the water-insoluble polyfunctional epoxy compound is at least one selected from polypropylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether. ..