JP2019116599A - Ink set - Google Patents

Abstract

To provide an ink set using an ink excellent in storage stability, and capable of obtaining a printed matter excellent in scratch resistance and image quality even by layering the ink, and to provide an inkjet recording method.SOLUTION: [1] There is provided an ink set containing inks with at least each color of cyan, yellow and magenta, the inks with each color is one of an ink (A) or an ink (B) satisfying following conditions, in which there is no case that all inks with each color correspond to the ink (A) or all inks correspond to the ink (B). [Conditions of ink (A) and ink (B)] The ink (A) and the ink (B) are water-based inks by dispersing a pigment into a water-based medium by polymer, the polymer is a water-insoluble crosslinked polymer manufactured by crosslinking a polymer having an acid value of 140 to 260 mgKOH/g by a crosslinking agent, a remaining acid value of the water-insoluble crosslinked polymer in the ink (A) is 78 to 100 mgKOH/g, and a remaining acid value of the water-insoluble crosslinked polymer in the ink (B) is 56 to 78 mgKOH/g.SELECTED DRAWING: None

Description

  The present invention relates to an ink set and an inkjet recording method.

The inkjet recording method is a method in which ink droplets are directly ejected from a very fine nozzle onto a recording medium and adhered to obtain characters and images. This method is extremely popular because it has many advantages such as easy full color and inexpensive, usable plain paper as the recording medium, and non-contact with the recording medium. In recent years, from the viewpoint of weather resistance and water resistance of recorded matter, those using a pigment as a colorant have become mainstream.
However, the pigment ink generally has a problem that the dispersion stability of the pigment particles in the aqueous medium is poor, and the pigment particles are aggregated to easily deteriorate the storage stability.

On the other hand, in addition to printing on a conventional highly absorbent recording medium called ordinary paper or copy paper, a low liquid absorption coated paper such as offset coated paper, or polyvinyl chloride resin, polypropylene resin, polyester resin There is a demand for printing on recording media for commercial printing using a film of a non-liquid-absorbent resin, etc.
When printing is performed by the inkjet recording method on these low liquid absorption and non liquid absorption recording media, it takes a long time to dry because absorption of the liquid component is slow or not absorbed, and color mixing tends to occur, and printing is performed. It is known that the initial scratch resistance is poor. In addition, unlike ordinary paper in which pigment penetrates into the paper, the low liquid absorption and non liquid absorption recording medium has pigment particles remaining on the paper, and it has poor abrasion resistance after drying because it receives direct external force. It is known.
Furthermore, when recording is repeated using color ink, the image may have blur or the abrasion resistance may be deteriorated.

Various ink sets have been proposed to solve these problems.
For example, Patent Document 1 discloses, as an ink set excellent in color reproducibility of red, blue or green, a treatment liquid containing an aggregating agent, and a resin-coated pigment coated with a pigment by a cross-linked water-soluble resin. The yellow, magenta and cyan inks containing a polymerizable compound and water are included, and two colors are superimposed to form an image, and the content and mass ratio of each pigment [crosslinked water-soluble resin / pigment] are specified. An ink set in the range is disclosed.
In Patent Document 2, as an ink set in which kogation of the pigment in the recording head is prevented, the dispersibility of the pigment in the ink is enhanced, and the landing accuracy is improved, the pigment and the acid value of 100 to 160 mg KOH / g Provided with an aqueous ink containing a (meth) acrylate copolymer having one of the following: one of the inks is a cyan ink containing a phthalocyanine compound, and the cyan ink is contained in the other inks An ink set is disclosed having an acid value of 0.7 to 0.95 times that of the copolymer.
In Patent Document 3, as an ink set capable of forming high image quality while suppressing mist contamination of a recording head, pigment particles covered with a non-crosslinked resin are dispersed in a plurality of types of ink, and the ink There is disclosed an ink set including a first ink in which the acid value of the resin is 100 to 180 mg KOH / g and a second ink in which the acid value of the resin is 60 to 90 mg KOH / g.

JP 2012-162655 A Unexamined-Japanese-Patent No. 2015-052057 JP, 2016-199684, A

However, in the ink set of Patent Document 1, although the scratch resistance is improved, the use of the polymerizable compound and the irradiation of the active energy ray become necessary, and the versatility is lost. Further, the techniques of Patent Documents 2 and 3 are sufficiently satisfied with respect to the abrasion resistance when applied to printing on a low liquid absorption non-liquid absorption recording medium, and the deterioration of image quality in double overstrike. It was not possible.
An object of the present invention is to provide an ink set and an ink jet recording method capable of obtaining a recorded matter excellent in abrasion resistance and image quality even when the ink having excellent storage stability is used and the ink is repeatedly ejected. I assume.

The present inventor uses an ink having a pigment dispersed with a water-insoluble cross-linked polymer formed by cross-linking a high acid number polymer in an ink set having two or more types of ink, and an ink having a relatively high acid number polymer It has been found that the above problems can be solved by using in combination an ink having a relatively low acid value polymer.
That is, the present invention provides the following [1] and [2].
[1] An ink set containing at least ink of each color of cyan, yellow, and magenta, wherein the ink of each color falls under either ink (A) or ink (B) satisfying the following conditions, and An ink set in which all the ink of each color does not correspond to the ink (A) or all the ink does not correspond to the ink (B).
Condition of Ink (A) or Ink (B)
The ink (A) and the ink (B) are aqueous inks in which a pigment is dispersed in an aqueous medium with a polymer, and the polymer is obtained by crosslinking a polymer having an acid value of 140 mg KOH / g or more and 260 mg KOH / g or less with a crosslinking agent. Water-insoluble crosslinked polymer
The residual acid value of the water-insoluble crosslinked polymer in the ink (A) is 78 mg KOH / g or more and less than 100 mg KOH / g, and the residual acid value of the water-insoluble crosslinked polymer in the ink (B) is 56 mg KOH / g or more and less than 78 mg KOH / g.
[2] An ink jet recording method for recording on a low liquid absorption recording medium using the ink set described in the above [1].

  According to the ink set and the inkjet recording method of the present invention, even if the ink excellent in storage stability is used and the ink is over-strapped, it is possible to obtain the recorded matter excellent in the scratch resistance and the image quality.

[Ink set]
The ink set of the present invention is an ink set containing at least cyan, yellow, and magenta inks, and the inks of each color are either ink (A) or ink (B) satisfying the following conditions. An ink set that does not correspond to all ink of each color corresponding to ink (A) or does not correspond to ink (B).
Condition of Ink (A) or Ink (B)
The ink (A) and the ink (B) are aqueous inks in which a pigment is dispersed in an aqueous medium with a polymer, and the polymer is obtained by crosslinking a polymer having an acid value of 140 mg KOH / g or more and 260 mg KOH / g or less with a crosslinking agent. Water-insoluble crosslinked polymer
The residual acid value of the water-insoluble crosslinked polymer in the ink (A) is 78 mg KOH / g or more and less than 100 mg KOH / g, and the residual acid value of the water-insoluble crosslinked polymer in the ink (B) is 56 mg KOH / g or more and less than 78 mg KOH / g.
The ink set of the present invention uses an ink excellent in storage stability, and even when the ink is over-printed, a recorded matter excellent in scratch resistance and image quality can be obtained, and the ink used is an inkjet recording method It is preferable to use as an ink set for inkjet recording, since it is excellent in discharge stability in the above.

In the present specification, the following terms have the following meanings.
-"Water-based medium" means a medium in which water occupies the largest proportion in the medium in which the pigment is dispersed, and "water-based ink" means that the content of water in the ink is 40% by mass or more. Mean ink.
"Recording" is a concept including printing for printing characters and images, and "recording" is a concept including printed matter and printed matter on which characters and images are recorded.
"Overprinting" means to print by recording a plurality of types of ink in the same range of a recorded matter in order to express secondary colors and tertiary colors.

The ink set of the present invention uses an ink excellent in storage stability, and even when the ink is over-strapped, it is possible to obtain a recorded matter excellent in abrasion resistance and image quality. Although the reason is not clear, it is considered as follows.
In the inks (A) and (B) in the ink set of the present invention, a high acid value polymer having an acid value of 140 mg KOH / g or more and 260 mg KOH / g or less is adsorbed on the pigment surface, and the polymer is crosslinked. As a result, the density of the crosslinking points is increased, and the polymer can form a sufficient three-dimensional network structure, so it is presumed that the swelling of the polymer by the solvent or the like in the ink is suppressed. Therefore, the polymer is not easily detached from the pigment, and the electrostatic repulsion between the pigment particles is increased to suppress aggregation, whereby the particle size of the pigment particles in the ink is stably maintained, and the storage stability of the ink Is considered to be maintained.
The ink set of the present invention comprises an ink (A) in which a pigment is dispersed with a water-insoluble crosslinked polymer having a relatively high residual acid number, and at least an ink (A) with a pigment. It comprises with the ink (B) disperse | distributed by the water insoluble crosslinked polymer with comparatively low value. The ink (A) is likely to spread dots after landing on the recording medium, but the ink (B) is characterized in that the dots are difficult to spread. At least with respect to the ink to be subjected to the overstrike, it is possible to enhance the particle size stability of the pigment particles described above and to construct the inks (A) and (B) which are excellent in storage stability. It is considered that the features are exhibited on the recording medium. Then, the unevenness which tends to be generated between the dots of the ink (B) can be appropriately filled with the ink (A), and by forming a smooth ink film on the recording medium, when the scratch resistance and the image quality are improved. Conceivable.

The inks of each color of cyan, yellow and magenta used in the ink set of the present invention correspond to either ink (A) or ink (B), and all the inks of each color correspond to ink (A) Or all the ink does not correspond to the ink (B). The ink (A) and the ink (B) are water-based inks in which a pigment is dispersed in a water-based medium with a water-insoluble crosslinked polymer.
In the ink set of the present invention, it is preferable that the ink (A) and the ink (B) be inks to be over-strapped. The order in which the ink (A) and the ink (B) are recorded on the recording medium is not limited, and recording may be performed in any order, but recording is first performed with the ink (B) and then recording with the ink (A) It is more preferable to do.
The ink set of the present invention can also be loaded with other inks than the cyan, magenta, and yellow three-color inks, but the other inks necessarily correspond to the ink (A) or the ink (B). It does not have to be However, it is preferable that all the ink is an ink set consisting only of the ink corresponding to either the ink (A) or the ink (B), that all the ink corresponds to the ink (A), or all the inks Is preferably an ink set that does not correspond to the ink (B).

<Pigment>
The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and lake pigments and fluorescent pigments can also be used. In addition, if necessary, they may be used in combination with an extender pigment.
Specific examples of the inorganic pigment include carbon black, titanium oxide, iron oxide, iron oxide, metal oxides such as iron oxide and chromium oxide, and pearlescent pigments. Particularly in the case of black ink, carbon black is preferred. As carbon black, furnace black, thermal lamp black, acetylene black, channel black etc. are mentioned.
Specific examples of the organic pigment include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments and chelate azo pigments; phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, iso indo dyes Polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and Sureren pigments, and the like can be mentioned.
The hue should have at least three colors of cyan, magenta and yellow, and the other colors are not particularly limited, and any chromatic pigment such as blue, red, orange and green can be used.
Specific examples of preferred organic pigments include C.I. I. Pigment yellow, C.I. I. Pigment red, C.I. I. Pigment orange, C.I. I. Pigment violet, C.I. I. Pigment blue, and C.I. I. And at least one product selected from pigment and green. In the case of overstrike ink, at least three colors of cyan, magenta and yellow are C.I. I. Pigment blue, C.I. I. Pigment red, C.I. I. It is preferable to select three types of pigment yellow.
Examples of the extender pigment include silica, calcium carbonate, talc and the like.
The above pigments may be used alone or in combination of two or more.

In the present invention, the pigment is contained in the ink as a pigment dispersed with a water-insoluble crosslinked polymer, or a water-insoluble crosslinked polymer particle containing a pigment.
The pigment is a water-insoluble crosslinked polymer particle containing a pigment (hereinafter simply referred to as "pigment-containing crosslinked polymer") from the viewpoint of improving particle diameter stability of the pigment particle and improving the abrasion resistance of the recorded matter and image quality while maintaining water resistance. It is preferable to contain as "polymer particle | grain".

<Polymer>
The ink (A) and the ink (B) in the ink set of the present invention are an aqueous ink in which a pigment is dispersed in an aqueous medium with a polymer, and the polymer has an acid value of 140 mg KOH / g or more and 260 mg KOH / g or less Hereinafter, it is a water-insoluble crosslinked polymer formed by crosslinking the "pre-crosslinking polymer" with a crosslinking agent.
The pre-crosslinking polymer is preferably a polymer having a carboxy group, and may be either a water-soluble polymer or a water-insoluble polymer, but is preferably a water-insoluble polymer.
Some of the carboxy groups of the polymer before crosslinking are crosslinked by a crosslinking agent to form a crosslinked structure. Even if the polymer having a carboxy group is a water soluble polymer, it becomes water insoluble due to crosslinking.
The term "water-insoluble polymer" means a polymer which does not become transparent when dispersed in water, specifically, a polymer which has been dried at 105 ° C. for 2 hours and which has reached a constant weight, is 25 ° C. The polymer is dissolved in less than 10 g, preferably less than 5 g, more preferably less than 1 g when dissolved in 100 g of deionized water until saturated.
On the other hand, the "water-soluble polymer" refers to a polymer having a dissolution amount of 10 g or more under the above conditions.
When the polymer is an anionic polymer, the amount is the dissolution amount when the anionic group of the polymer is 100% neutralized with NaOH.

The water-insoluble crosslinked polymer is formed in an aqueous medium by dispersing the pigment in an aqueous medium in the state where at least a part of the pre-crosslinked polymer having a carboxy group is neutralized with a neutralizing agent, and then crosslinking with a crosslinking agent. Is preferred. Although this does not isolate the water-insoluble crosslinked polymer, it can be adjusted in relation to the polymer's monomer configuration, molecular weight, type and amount of neutralizing agent, and type and amount of crosslinking agent.
The acid value of the polymer before crosslinking is preferably 145 mg KOH / g or more, more preferably 150 mg KOH / g or more, still more preferably 170 mg KOH / g, from the viewpoint of improving the storage stability of the ink and the abrasion resistance of the recorded matter and the image quality. It is not less than g, and preferably not more than 255 mg KOH / g, more preferably not more than 250 mg KOH / g, still more preferably not more than 245 mg KOH / g.
If the acid value is in the above range, the amount of carboxy group and carboxy group to be neutralized is sufficient, and the dispersion stability of the pigment is ensured. It is also preferred from the viewpoint of the balance between the affinity of the polymer and the aqueous medium and the interaction between the polymer and the pigment.
The acid value of the polymer can be determined by the titration method described in the examples. Moreover, it can also calculate from the mass ratio of the monomer to comprise.

The form of presence of the pigment and the water-insoluble crosslinked polymer in the water-based ink includes the form in which the water-insoluble crosslinked polymer is adsorbed to the pigment and the form in which the water-insoluble crosslinked polymer contains the pigment (encapsulates the pigment) Particle forms, including particle forms in which pigments are uniformly dispersed), and forms in which pigments are not adsorbed. From the viewpoint of dispersion stability of the pigment, in the present invention, the form of polymer particles (pigment-containing crosslinked polymer particles) in which the water-insoluble crosslinked polymer contains the pigment is preferable, and the particle form containing the pigment and containing the pigment is More preferable.
The polymer has a function as a pigment dispersant which exhibits a pigment dispersing action and a function as a fixing agent to a recording medium.

(Polymer before crosslinking)
The polymer before crosslinking includes one or more selected from polyesters, polyurethanes, and vinyl polymers, but from the viewpoint of improving the storage stability of aqueous ink, it is selected from vinyl compounds, vinylidene compounds, and vinylene compounds 1 Preferred are vinyl polymers obtained by addition polymerization of vinyl monomers of species or more.
The vinyl polymer includes (a) a carboxy group-containing vinyl monomer (hereinafter also referred to as "component (a)") and (b) a hydrophobic vinyl monomer (hereinafter referred to as "component (b)"). Preferred are vinyl polymers obtained by copolymerizing a vinyl monomer mixture (hereinafter, also simply referred to as "monomer mixture"). The vinyl polymer has a constituent unit derived from the component (a) and a constituent unit derived from the component (b). The vinyl polymer is further derived from a structural unit derived from (c) a macromonomer (hereinafter also referred to as "component (c)") or (d) a nonionic monomer (hereinafter referred to as "component (d)"). It can contain a structural unit.

[(A) Carboxy group-containing vinyl monomer]
The (a) carboxy group-containing vinyl monomer is used as a monomer component of a polymer from the viewpoint of improving the dispersion stability of the pigment-containing crosslinked polymer particles in the aqueous ink. Examples of carboxy group-containing vinyl monomers include carboxylic acid monomers.
Preferred examples of the carboxylic acid monomer include one or more selected from acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethyl succinic acid, etc. And one or more selected from methacrylic acid is more preferable.

[(B) hydrophobic vinyl monomer]
The hydrophobic vinyl monomer (b) is used as a monomer component of the polymer from the viewpoint of enhancing the adsorptivity of the polymer to the pigment and improving the dispersion stability of the pigment-containing crosslinked polymer particles in the aqueous ink. As a hydrophobic vinyl monomer, the alkyl (meth) acrylate which has a C1-C22 alkyl group or C6-C22 aryl group, an aromatic group containing monomer etc. are mentioned preferably.
The alkyl (meth) acrylate is preferably one having an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate and 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 Rate, isododecyl (meth) acrylate, isostearyl (meth) acrylate.
In addition, "(meth) acrylate" means 1 or more types chosen from an acrylate and a methacrylate. "(Meta)" in the following is also synonymous.

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having a molecular weight of less than 500, preferably having 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and a styrenic monomer, Aromatic group-containing (meth) acrylates are more preferred.
As the styrene-based monomer, styrene, α-methylstyrene, vinyl toluene and divinylbenzene are preferable, and styrene and α-methylstyrene are more preferable.
Moreover, as aromatic group containing (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate etc. are preferable, and benzyl (meth) acrylate is more preferable.
As the hydrophobic monomer (b), two or more of the above-mentioned monomers may be used, and a styrenic monomer and an aromatic group-containing (meth) acrylate may be used in combination.

[(C) macromonomer]
(C) The macromonomer is a compound having a number average molecular weight of 500 to 100,000 having a polymerizable functional group at one end, and may be used as a monomer component of a polymer from the viewpoint of improving the dispersion stability of an aqueous ink it can. The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group.
The number average molecular weight of the (c) macromonomer is preferably 1,000 or more and 10,000 or less. The number average molecular weight is measured by gel permeation chromatography using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
From the viewpoint of improving the dispersion stability of the water-based ink, the (c) macromonomer is preferably an aromatic group-containing monomer-based macromonomer and a silicone-based macromonomer, and more preferably an aromatic group-containing monomer-based macromonomer.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer macromonomer include the aromatic group-containing monomers described in the (b) hydrophobic monomer, and styrene and benzyl (meth) acrylate are preferable, and styrene is More preferable.
As an example of a styrene system macromonomer, AS-6 (S), AN-6 (S), HS-6 (S) (brand name of Toagosei Co., Ltd.) etc. are mentioned.

[(D) nonionic monomer]
For the polymer, from the viewpoint of improving the dispersion stability of the water-based ink, (d) a nonionic monomer can be further used as a monomer component.
(D) As the nonionic monomer, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (n = 2 to 30, n represents an average added mole number of oxyalkylene group. The same) polyalkylene glycol (meth) acrylates such as (meth) acrylates, polyethylene glycol (n = 2 to 30) (meth) acrylates, alkoxypolyalkylene glycols such as methoxypolyethylene glycols (n = 1 to 30) (meth) acrylate (Meth) acrylate, phenoxy (ethylene glycol / propylene glycol copolymer) (n = 1 to 30, ethylene glycol in it: n = 1 to 29) (meth) acrylate, etc. may be mentioned. Among these, polypropylene glycol (n = 2 to 30) (meth) acrylate and phenoxy (ethylene glycol propylene glycol copolymerization) (meth) acrylate are preferable, and polypropylene glycol (n = 2 to 30) (meth) acrylate is More preferable.

Specific examples of the commercially available component (d) include NK esters M-20G, 40G, 90G, 230G, etc. of Shin-Nakamura Chemical Co., Ltd., Blenmer PE-90 of NOF Corporation, etc. 200, 350, etc., PME-100, 200, 400, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, etc., 50 PEP-300, 50 POEP-800 B, 43 PAPE-600 B Etc.
The said (a)-(d) component can be used individually or in mixture of 2 or more types, respectively.
As mentioned above, the pre-crosslinking polymer having a carboxy group used in the present invention has a structural unit derived from at least one (a) carboxy group-containing vinyl monomer selected from acrylic acid and methacrylic acid, and 1 to 22 carbon atoms Vinyl polymer containing a structural unit derived from at least one (b) hydrophobic vinyl monomer selected from an acrylate monomer having an alkyl group of 6 or more and an aryl group having 6 to 22 carbon atoms, a methacrylate monomer and an aromatic group-containing monomer Is preferred.

(Content of each component or constitutional unit in monomer mixture or polymer)
The content of the component (a) is preferably 10% by mass or more, more preferably 12% by mass or more, still more preferably 15% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less More preferably, it is 40% by mass or less.
The content of the component (b) is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 88% by mass or less More preferably, it is 85% 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 The content is preferably 25% by mass or less, 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 The content is more preferably 35% by mass or less, still more preferably 30% by mass or less.

The mass ratio of [(a) component / (b) component] is preferably 0.1 or more, more preferably 0.15 or more, still more preferably 0.2 or more, and preferably 1.5 or less. More preferably, it is 1.2 or less, more preferably 1 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, Preferably it is 0.5 or more, Preferably it is 1.5 or less, More preferably, it is 1.0 or less, More preferably, it is 0.8 or less.

(Production of polymer before crosslinking)
The polymer before crosslinking is produced by copolymerizing the monomer mixture by a known polymerization method such as bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method and the like. Among these polymerization methods, the solution polymerization method is preferred.
The solvent used in the solution polymerization method is not particularly limited, but a polar organic solvent is preferred. When the polar organic solvent is miscible with water, it can also be used by mixing with water. 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 them 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 and a polymerization chain transfer agent can be used.
As a polymerization initiator, azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), t-butyl peroxy octoate, benzoyl peroxide, etc. Known radical polymerization initiators such as organic peroxides of the above can be used. The amount of the radical polymerization initiator is preferably 0.001 to 5 moles, more preferably 0.01 to 2 moles per mole of the monomer mixture.
As the polymerization chain transfer agent, known chain transfer agents such as mercaptans such as octyl mercaptan and 2-mercaptoethanol, and thiuram disulfides can be used.
Also, there is no limitation on the mode of chain of the polymerization monomers, and any polymerization mode such as random, block, graft and the like may be used.

The preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent, etc., but usually the polymerization temperature is preferably 30 ° C. or more, more preferably 50 ° C. or more, and preferably 95 ° C. or less. More preferably, it is 80 ° C. or less. 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, solvent evaporation and the like. In addition, the obtained polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatography, extraction and the like.
In the present invention, as a method of dispersing the pigment using a polymer, any known method can be used, but it is preferable to use an aqueous dispersion of the pigment-containing crosslinked polymer particles described later. From the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing crosslinked polymer particles, the polymer used as it is in order to use the contained organic solvent as the organic solvent used in step I described later without removing the solvent used in the polymerization reaction. It is preferable to use as a solution.
The solid content concentration of the 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 crosslinked polymer particles. The following content is more preferably 65% by mass or less.

The number average molecular weight of the pre-crosslinking polymer used in the present invention is preferably 2,000 or more, more preferably 5,000 or more, and preferably 20,000 or less, more preferably 18,000 or less. If the molecular weight of the polymer is in the above range, the adsorptive power to the pigment is sufficient, and dispersion stability can be exhibited.
In addition, the measurement of a number average molecular weight can be performed by the method as described in an Example.

[Production of pigment-containing crosslinked polymer particles]
The water-insoluble crosslinked polymer particles containing a pigment can be efficiently produced as a water-based pigment dispersion by a method having the following step I, step II and step III.
Step I: A mixture containing a polymer before crosslinking, an organic solvent, a neutralizing agent, a pigment, and water (hereinafter also referred to as “pigment mixture”) is subjected to dispersion treatment to obtain pigment-containing polymer particles (hereinafter “pigment-containing” Step of obtaining a dispersion of polymer particles ") Step II: Water dispersion of pigment-containing polymer particles after removing the organic solvent from the dispersion obtained in step I (hereinafter," pigment water dispersion A " Step III: Step III: Water-based pigment containing water-insoluble crosslinked polymer particles (pigment-containing crosslinked polymer particles) obtained by crosslinking the pigment water dispersion A obtained in Step II with a crosslinking agent and containing the pigment Process for obtaining a dispersion (hereinafter, also referred to as "water-based pigment dispersion B")

(Step I)
In step I, first, the polymer before crosslinking is dissolved in an organic solvent, and further, a neutralizing agent, a pigment, water, and, if necessary, a surfactant and the like are added to the obtained organic solvent solution and mixed. Preferred is a method of obtaining an oil-type dispersion. There is no particular limitation on the order of mixing the organic solvent solution of the polymer before crosslinking, the neutralizing agent, the pigment, water and the like, but dissolving the polymer before crosslinking in the organic solvent and adding the neutralizing agent, water and pigment in this order Is preferred.
The organic solvent to be used is not limited, but aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, esters and the like are preferable, and the wettability to the pigment, the solubility of the polymer, and the adsorption to the pigment of the polymer From the viewpoint of improving the properties, ketones having 4 to 8 carbon atoms are more preferable, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is still more preferable.
When the polymer before crosslinking is synthesized by a solution polymerization method, the solvent used in the polymerization may be used as it is.

(Neutralization)
Preferably, at least a portion of the carboxy groups of the precrosslinked polymer are neutralized. The pH of the obtained water-based ink is preferably 5.5 or more, more preferably 6 or more from the viewpoint of handleability to reduce skin irritation and the like, and preferably from the viewpoint of suppressing corrosion of members. It is 12 or less, more preferably 11 or less, and still more preferably 10 or less.
Examples of the neutralizing agent include alkali metal compounds and ammonia. Examples of the alkali metal compound include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide, with sodium hydroxide and potassium hydroxide being preferred. Also, the polymer may be neutralized in advance.
The neutralizing agent is preferably used as an aqueous neutralizing agent solution from the viewpoint of promoting the neutralization sufficiently and uniformly. The concentration of the aqueous neutralizing agent solution is preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more from the above viewpoint, and preferably 50% by mass or less, more preferably It is 25 mass% or less.

The use equivalent of the neutralizing agent (the degree of neutralization of the polymer) is preferably 10 mol% or more, more preferably 20 mol% or more, and still more preferably 30 mol% or more from the viewpoint of storage stability of the obtained aqueous ink And preferably 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less.
Here, the use equivalent of the neutralizing agent can be determined by the following equation.
Use equivalent of neutralizing agent (mol%) = [[addition mass of neutralizing agent (g) / equivalent of neutralizing agent] / [acid value of polymer (mg KOH / g) x mass of polymer (g) / (56 × 1000)]] × 100
When the usage equivalent of the neutralizing agent is 100 mol% or less, the usage equivalent is the same as the neutralization degree, and when the usage equivalent of the neutralizing agent in the above formula exceeds 100 mol%, the neutralizing agent is a polymer It means that it is in excess with respect to the carboxy group, and in this case, the degree of neutralization is regarded as 100 mol%.

(Content of each component in pigment mixture)
The content of each component in the pigment mixture is as follows from the viewpoint of the storage stability of the obtained aqueous pigment dispersion and the productivity.
The content of the pigment in step I in the pigment mixture is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 12.5% by mass or more, and preferably 35% by mass or less, more preferably Preferably it is 30 mass% or less, More preferably, it is 20 mass% or less.
The content of the polymer before crosslinking in the pigment mixture is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and preferably 8% by mass or less, more preferably 7%. It is at most mass%, more preferably at most 6 mass%.
The content of the organic solvent in the pigment mixture is preferably 5% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass. % Or less, more preferably 25% by mass or less.
The content of water in the pigment mixture is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass The content is more preferably 75% by mass or less.

  The mass ratio of the pigment to the pre-crosslinking polymer in the pigment mixture [pigment / pre-crosslinking polymer] is preferably 40/60 or more, more preferably from the viewpoint of further improving the storage stability and redispersibility of the obtained aqueous pigment dispersion. It is preferably 50/50 or more, more preferably 60/40 or more, and preferably 95/5 or less, more preferably 90/10 or less, still more preferably 85/15 or less.

(Dispersion treatment of pigment mixture)
In step I, the pigment mixture is subjected to dispersion treatment to obtain a dispersion of pigment-containing polymer particles. There is no particular limitation on the dispersion method for obtaining the dispersion. The average particle diameter of the pigment particles can be finely divided to a desired particle diameter only by the main dispersion, but preferably, after the pigment mixture is predispersed, further shear stress is applied to carry out the main dispersion to obtain pigment particles. It is preferable to control so that the average particle diameter of.
The temperature in step I, in particular in the predispersion, is preferably 0 ° C. or more, and preferably 40 ° C. or less, more preferably 30 ° C. or less, still more preferably 25 ° C. or less. The dispersion time is preferably 0.5 hours or more, more preferably 0.8 hours or more, and preferably 30 hours or less, more preferably 10 hours or less, still more preferably 5 hours or less.
When the pigment mixture is predispersed, a commonly used mixing and stirring apparatus such as an anchor blade and a disper wing can be used, but among them, a high-speed stirring and mixing apparatus is preferable.

Examples of means for giving the shear stress of the present dispersion include kneaders such as a roll mill and a kneader, high pressure homogenizers such as a microfluidizer (manufactured by Microfluidic), and media type dispersers such as a paint shaker and a bead mill. As a commercially available media type dispersing machine, Ultra Apex Mill (manufactured by Kotobuki Industry Co., Ltd.), Picomill (manufactured by Asada Iron Works Co., Ltd.) and the like can be mentioned. These devices can also be combined. Among these, from the viewpoint of reducing the particle size of the pigment, it is preferable to use a high pressure homogenizer.
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 treatment pressure and the number of passes.
The treatment pressure is preferably 60 MPa or more, more preferably 100 MPa or more, still more preferably 130 MPa or more, and preferably 300 MPa or less, more preferably 250 MPa or less, from the viewpoint of productivity and economy.
The number of passes is preferably 3 or more, more preferably 10 or more, and preferably 30 or less, more preferably 25 or less.

(Step II)
In step II, an aqueous dispersion of pigment-containing polymer particles (pigment water dispersion A) can be obtained by removing the organic solvent from the dispersion obtained in step I by a known method. The organic solvent in the obtained pigment water dispersion A is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
Also, if necessary, the dispersion may be heated and stirred before distilling off the organic solvent.
The obtained pigment water dispersion A is one in which the pigment-containing polymer particles are dispersed in a medium containing water as a main medium. Here, the form of the pigment-containing polymer particle is not particularly limited as long as the particle is formed of at least the pigment and the polymer, but as described above, the particle form in which the pigment is contained in the polymer before crosslinking preferable.

The non-volatile component concentration (solid content concentration) of the obtained pigment water dispersion A is preferably 10% by mass or more from the viewpoint of improving the dispersion stability of the pigment water dispersion A and the viewpoint of facilitating the preparation of the water-based ink. More preferably, it is 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.
In addition, solid content concentration of the pigment water dispersion A is measured by the method as described in an Example.
The average particle diameter of the pigment-containing polymer particles in the pigment water dispersion A is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm, from the viewpoint of reducing coarse particles and improving discharge stability of the water-based ink. This is preferably 200 nm or less, more preferably 180 nm or less, and still more preferably 150 nm or less.
In addition, the average particle diameter of a pigment containing polymer particle is measured by the method as described in an Example.

(Step III)
In step III, the pigment water dispersion A obtained in step II is treated with a crosslinking agent from the viewpoint of improving the storage stability of the obtained aqueous pigment dispersion B and the aqueous ink, the scratch resistance of the recorded matter, and the image quality. A water-based pigment dispersion B is obtained which contains the water-insoluble crosslinked polymer crosslinked and crosslinked. In this step, a part of carboxy groups of the pre-crosslinking polymer constituting the pigment-containing polymer particles is crosslinked to form a crosslinked structure in the surface layer of the pigment-containing polymer particles. That is, the water-insoluble crosslinked polymer according to the present invention is obtained by the crosslinking reaction between the polymer before crosslinking and the crosslinking agent on the pigment surface, and the polymer before crosslinking contained in the pigment-containing polymer particles in the pigment water dispersion A is the crosslinking agent. To become a water insoluble crosslinked polymer crosslinked by
Thus, the aqueous pigment dispersion B of the present invention becomes an aqueous pigment dispersion containing pigment-containing crosslinked polymer particles in which the pigment is dispersed in an aqueous medium with the polymer dispersant according to the present invention.

<Crosslinking agent>
The crosslinking agent used in the present invention preferably has a water solubility of 50% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass, from the viewpoint of efficiently performing a crosslinking reaction in a medium mainly containing water. Preferred are water insoluble polyfunctional epoxy compounds which are as follows.
Here, the water solubility is the dissolution rate (% by mass) when 10 parts by mass of the crosslinking agent is dissolved in 90 parts by mass of water at room temperature 25 ° C. Specifically, it is measured by the method described in the Examples. Ru.

The water-insoluble polyfunctional epoxy compound is preferably a compound having two or more epoxy groups in a molecule, more preferably a compound having a glycidyl ether group, and still more preferably a polyvalent compound having a hydrocarbon group having 3 to 8 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, from the viewpoint of easiness of reaction and stability of the resulting crosslinked polymer, and preferably Is 2000 or less, more preferably 1500 or less, still more preferably 1000 or less.
The number of epoxy groups of the water-insoluble polyfunctional epoxy compound is preferably 2 or more per molecule from the viewpoint of efficiently cross-linking with a carboxy group to enhance the stability etc. of the pigment-containing crosslinked polymer particles, and the market availability. More preferably, it is 3 or more, and preferably 6 or less, more preferably 4 or less per molecule.
The epoxy equivalent of the water-insoluble polyfunctional epoxy compound is preferably 90 or more, more preferably 100 or more, still more preferably 110 or more, and preferably 300 or less, more preferably 220 or less, more preferably 160 or less. .

Specific examples of water-insoluble polyfunctional epoxy compounds include polypropylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, hydrogenation One or more selected from polyglycidyl ethers such as bisphenol A type diglycidyl ether and the like can be mentioned.
Among these, one or more selected from polypropylene glycol diglycidyl ether (water solubility 31%), trimethylolpropane polyglycidyl ether (water solubility 27%), and pentaerythritol polyglycidyl ether (water solubility 0%) are preferable.

(Crosslinking reaction)
The crosslinking reaction between the pre-crosslinking polymer and the crosslinking agent is preferably carried out after dispersing the pigment with the pre-crosslinking polymer.
The reaction temperature is preferably 40 ° C. or more, more preferably 50 ° C. or more, still more preferably 60 ° C. or more, and preferably 95 ° C. or less, more preferably 90 ° C. from the viewpoint of completion of the reaction and economy. It is below. The reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, still more preferably 2 hours or more, and preferably 12 hours or less, more preferably 10 hours, from the same viewpoint as above. It is less than time, more preferably less than 8 hours.
The crosslinking degree of the water-insoluble crosslinked polymer is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less More preferably, it is 60 mol% or less. The degree of crosslinking is the apparent degree of crosslinking calculated from the acid number of the polymer and the equivalent of the epoxy group of the crosslinking agent. That is, the degree of crosslinking is a percentage (mol%) of "the molar equivalent number of epoxy groups of the crosslinking agent / the molar equivalent number of carboxy groups of the polymer".

The average particle diameter of the pigment-containing crosslinked polymer particles in the water-based pigment dispersion B is preferably 50 nm or more, more preferably 60 nm or more, still more preferably from the viewpoint of reducing coarse particles and improving discharge stability of the water-based ink. It is 70 nm or more, and preferably 200 nm or less, more preferably 180 nm or less, and further preferably 150 nm or less.
The average particle size of the pigment-containing crosslinked polymer particles is measured by the method described in the examples.
Further, the average particle diameter of the pigment-containing crosslinked polymer particles in the water-based ink is the same as the average particle diameter of the pigment-containing crosslinked polymer particles in the water-based pigment dispersion B. It is the same as the preferred embodiment of the average particle size in B.

The pH of the resulting aqueous pigment dispersion B is preferably 8 or more. When the pH is 8 or more, dissociation of the anionic group is promoted, the charge amount of the pigment dispersion is sufficient, and the particle size stability of the pigment particles in the pigment dispersion can be enhanced. The pH of the aqueous pigment dispersion B is more preferably 8.5 or more, and the upper limit thereof is not particularly limited, but when the pH exceeds 11, the pH of the ink using the pigment dispersion becomes too high. It is not preferable because it adversely affects the members of the printer or printing machine using the ink. Therefore, the pH of the water-based pigment dispersion B is more preferably 10.5 or less.
Although there is no restriction | limiting in particular in the measuring method of pH, The pH measuring method using a glass electrode is prescribed | regulated to JISZ8802, and this method is preferable from a simple and accurate point. Specifically, it is measured by the method described in the examples.

[Water-based ink]
The ink set of the present invention contains at least three color inks of cyan, yellow and magenta, and the ink of each color corresponds to either ink (A) or ink (B), and all the inks of each color Does not correspond to the ink (A) or all the ink does not correspond to the ink (B).
The residual acid value of the water-insoluble crosslinked polymer in the ink (A) is from 78 mgKOH / g to less than 100 mgKOH / g from the viewpoint of improving the storage stability of the ink, the abrasion resistance of the recorded matter, and the image quality.
The residual acid value of the water-insoluble crosslinked polymer in the ink (A) is preferably 80 mg KOH / g or more, more preferably 81 mg KOH / g or more, still more preferably 82 mg KOH / g or more, and preferably 99 mg KOH / g or less, more preferably Preferably it is 98 mgKOH / g or less, More preferably, it is 97 mgKOH / g or less.

The residual acid value of the water-insoluble crosslinked polymer in the ink (B) is from 56 mg KOH / g to less than 78 mg KOH / g from the viewpoint of improving the storage stability of the ink, the abrasion resistance of the recorded matter, and the image quality.
The residual acid value of the water-insoluble crosslinked polymer in the ink (B) is preferably 57 mg KOH / g or more, more preferably 59 mg KOH / g or more, still more preferably 60 mg KOH / g or more, and preferably 76 mg KOH / g or less, more preferably Preferably it is 75 mgKOH / g or less, More preferably, it is 74 mgKOH / g or less.
The residual acid value of the water-insoluble crosslinked polymer in the ink is calculated by the following equation as the residual acid value after crosslinking.
Residual acid value of water-insoluble crosslinked polymer in ink (mg KOH / g)
= Acid value of polymer before crosslinking (mg KOH / g) x (100-Degree of crosslinking (mol%))
The difference between the residual acid number of the water-insoluble crosslinked polymer in the ink (A) and the residual acid number of the water-insoluble crosslinked polymer in the ink (B) appropriately fills the unevenness of the ink dots, and the scratch resistance and image quality of the recorded matter From the viewpoint of improving the pH, it is preferably 5 mg KOH / g or more, more preferably 10 mg KOH / g or more, still more preferably 15 mg KOH / g or more, and preferably 45 mg KOH / g or less, more preferably 40 mg KOH / g or less, more preferably Is 35 mg KOH / g or less.

The water-based pigment dispersion according to the present invention can be used as a water-based ink by adjusting the content of the organic solvent or water as it is or as required. The water-based ink according to the present invention contains water-insoluble crosslinked polymer particles containing the pigment, an organic solvent, and water.
The organic solvent is preferably at least one selected from polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds, and more preferably polyhydric alcohols and polyhydric alcohol alkyl ethers Or more preferably one or more selected from ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylol propane, and diethylene glycol diethyl ether, and still more preferably glycerol or triethylene. One or more selected from glycol and trimethylolpropane can be mentioned.

[Method of producing water-based ink]
The water-based ink according to the present invention can be efficiently produced by the method including the steps I to III and further the following step IV.
Step IV: A step of mixing the aqueous pigment dispersion B obtained in Step III with the organic solvent to obtain an aqueous ink There is no particular limitation on the method of mixing the aqueous pigment dispersion B and the organic solvent in Step IV.
The organic solvent in step IV is used from the viewpoint of further improving the storage stability and the like of the water-based ink. The organic solvent used here preferably contains one or more organic solvents having a boiling point of 90 ° C. or more, and an organic solvent having a weighted average of boiling points of 250 ° C. or less is preferable. The weighted average value of the boiling point of the organic solvent is preferably 150 ° C. or more, more preferably 180 ° C. or more, and preferably 240 ° C. or less, more preferably 220 ° C. or less, still more preferably 200 ° C. or less.
The polyhydric alcohol etc. are mentioned as a specific example of the said organic solvent.

In the method for producing an aqueous ink according to the present invention, if necessary, a humectant, a wetting agent, a penetrant, a dispersant, a surfactant, a viscosity modifier, an antifoamer, an antiseptic agent generally used for the aqueous ink. It is possible to add various additives such as mildew proofing agent, rust preventive agent and the like and further to carry out filtration treatment with a filter or the like.
The aqueous ink obtained by the above production method comprises an aqueous pigment dispersion B containing pigment-containing crosslinked polymer particles and water, and the organic solvent, and the organic solvent is preferably a polyhydric alcohol and polyhydric alcohol alkyl. The aqueous ink is one or more selected from ethers, more preferably one or more selected from glycerin, triethylene glycol, and trimethylolpropane.
The contents of the components of the water-based ink and the physical properties of the ink are as follows.

(Content of pigment)
The content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 2.5% by mass or more, from the viewpoint of improving the printing concentration of the water-based ink. Further, from the viewpoint of lowering the ink viscosity at the time of solvent evaporation and further improving the storage stability, it is preferably 15% by mass or less, more preferably 10% by mass or less, and further preferably 7% by mass or less.
(Total content of pigment and water insoluble crosslinked polymer)
The total content of the pigment and the water-insoluble crosslinked polymer in the aqueous ink is preferably 2% by mass or more, more preferably 3% by mass or more, still more preferably 4% by mass or more, still more preferably 5% by mass or more And preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, still more preferably 8% by mass or less.

(Physical properties of water-based ink)
The viscosity of the aqueous ink at 32 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, and still more preferably 5.0 mPa · s or more from the viewpoint of further improving the storage stability of the ink. And preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, still more preferably 7.0 mPa · s or less.
From the viewpoint of further improving the storage stability of the ink, the pH of the water-based ink is preferably 7.0 or more, more preferably 7.2 or more, and still more preferably 7.5 or more. The pH is preferably 11.0 or less, more preferably 10.0 or less, and even more preferably 9.5 or less from the viewpoint of resistance to a member and skin irritation.

[Ink jet recording method]
The ink jet recording method of the present invention is a method of recording on a low liquid absorption recording medium using the ink set of the present invention.
In the ink jet recording method of the present invention, it is preferable to overstrike the ink (A) and the ink (B) loaded in the ink set of the present invention, and the ink loaded in the ink set is the ink (A) or the ink An ink is used that corresponds to any of (B) and that all the inks correspond to the ink (A) or all the inks do not correspond to the ink (B).

Examples of the low liquid absorbing recording medium used in the present invention include low liquid absorbing coated paper and resin film, which may be a sheet or a roll, but from the viewpoint of productivity, a roll-shaped recording medium Is preferred. It is preferable to use a recording medium which does not undergo pretreatment such as applying a treatment liquid as the low liquid absorption recording medium used in the present invention.
As coated paper, general purpose glossy paper “OK Top Coat Plus” (manufactured by Oji Paper Co., Ltd., the amount of water absorbed at a contact time of 100 ms (the same applies hereinafter) 4.9 g / m ² ), multicolor foam gloss paper (Oji Paper Co., Ltd. And water absorption amount of 5.2 g / m ² ), UPMF inesse Gloss (manufactured by UPM, water absorption amount of 3.1 g / m ² ), and the like.
A transparent synthetic resin film is mentioned as a resin film, For example, a polyester film, a vinyl chloride film, a polypropylene film, a polyethylene film, a nylon film etc. are mentioned. These films may be biaxially stretched films, uniaxially stretched films, or non-stretched films. Among these, polyester films and stretched polypropylene films are more preferable, polyester films such as polyethylene terephthalate (PET) film treated with corona discharge, and stretched polypropylene films such as biaxially oriented polypropylene (OPP) film treated with corona discharge More preferable.

In the present invention, any recording head of serial head type and line head type can be used, but line head type is preferable. The line head method is a method in which the head is fixed, the recording medium is moved in the transport direction, ink droplets are ejected from the nozzle openings of the head in conjunction with the movement, and the ink adheres to the recording medium. It can be recorded by one pass method.
The discharge method of the ink droplet is preferably a piezo method. In the piezo method, a large number of nozzles are in communication with the pressure chambers, and ink droplets are ejected from the nozzles by vibrating the wall surfaces of the pressure chambers with piezo elements. A thermal method can also be adopted.

  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 polymer Gel chromatography method using a solution of phosphoric acid and lithium bromide dissolved in N, N-dimethylformamide so as to have concentrations of 60 mmol / L and 50 mmol / L, respectively, as an eluent. Molecular weight is known as a standard substance by [Tosoh GPC apparatus (HLC-8320GPC), Tosoh Corporation column (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn SuperAW-H), flow rate: 0.5 mL / min] Monodispersed polystyrene kit [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A- 500), manufactured by Tosoh Corp.].

(2) Measurement of acid value of polymer Dissolve the resin in a titration solvent in which toluene and acetone (2 + 1) are mixed in a potentiometric automatic titrator (manufactured by Kyoto Denshi Kogyo Co., Ltd., motorized burette, model number: APB-610), and conduct potentiometric titration It titrated with the 0.1N potassium hydroxide / ethanol solution by the method, and made the inflexion point on the titration curve the end point. The acid number was calculated from the titer to the end of the potassium hydroxide solution.

(3) Measurement of average particle diameter of pigment-containing (crosslinked) polymer particles Cumulant analysis was performed using a laser particle analysis system "ELSZ-1000" (manufactured by Otsuka Electronics Co., Ltd.) to measure the cumulant average particle diameter. The measurement conditions were a temperature of 25 ° C., an angle of 165 ° between the incident light and the detector, and an integration count of 100. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. It diluted with water so that a measurement density | concentration might be 5 * 10 < ^-3 > mass% (solid content concentration conversion), and it carried out.

(4) Measurement of solid content concentration of pigment water dispersion In a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), 10.0 g of sodium sulfate which was constantized in a desiccator was weighed, and a sample of about 1. Add 0 g, mix, weigh accurately, maintain volatile environment at 105 ° C, gauge pressure-0.08MPa for 2 hours to remove volatiles, and then remove at room temperature (25 ° C) desiccator It was left for 15 minutes and the mass was measured. The mass of the sample after devolatilization was regarded as solid content, and was divided by the mass of the added sample to obtain solid concentration.

(5) Measurement of water solubility of crosslinking agent 90 parts by mass of ion exchange water and 10 parts by mass of crosslinking agent (W1) are added to a glass tube (25 mmφ × 250 mmh) at room temperature 25 ° C., and the glass tube is heated to 25 ° C. It stood still in the adjusted thermostat for 1 hour. Then, the glass tube was vigorously shaken for 1 minute and then allowed to stand again in a thermostat for 12 hours. Next, the undissolved material separated from water and precipitated or suspended was collected, dried at 40 ° C. under a gauge pressure of −0.08 MPa for 6 hours, and weighed (W 2). The water solubility (mass%) was calculated by the following formula.
Water solubility rate (mass%) = {(W1-W2) / W1} × 100

(6) Measurement of pH of pigment water dispersion A and water-based pigment dispersion B Desktop type pH meter "F-71" (made by HORIBA, Ltd.) using pH electrode "6337-10D" (made by HORIBA, Ltd.) The pH of the dispersion at 20 ° C. was measured using

<Synthesis of polymer>
Synthesis example 1
Acrylic acid (Wako Pure Chemical Industries, Ltd., reagent) 61.5 parts, Styrene (Wako Pure Chemical Industries, Ltd. reagent) 129.5 parts, α-methylstyrene (Wako Pure Chemical Industries, Ltd., reagent) 9 .0 parts were mixed to prepare a monomer mixture. In a reaction vessel, 20 parts of methyl ethyl ketone (MEK), 0.3 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were added and mixed, and nitrogen gas substitution was sufficiently performed.
On the other hand, the remaining 90% of the monomer mixture, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK, and an azo-based radical polymerization initiator (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65) in a dropping funnel. A mixed solution of 2.2 parts of 2,2′-azobis (2,4-dimethylvaleronitrile)) is added, and the temperature of the monomer mixture in the reaction vessel is raised to 65 ° C. with stirring under a nitrogen atmosphere, and then added dropwise. The mixture in the funnel was dropped over 3 hours. A solution of 0.3 part of the above-mentioned polymerization initiator in 5 parts of MEK is added after 2 hours of lapse at 65 ° C. from the end of dropwise addition, followed by aging for 2 hours at 65 ° C. for 2 hours at 70 ° C. (A) (Number average molecular weight of polymer: 12000, acid value: 240 mg KOH / g) was obtained.

Synthesis Example 2, Comparative Synthesis Example 1
Polymer solutions (b) and (c) were obtained in the same manner as in Synthesis Example 1 except that the mixing amounts of acrylic acid, styrene and α-methylstyrene were changed as shown in Table 1 in Synthesis Example 1. The results are shown in Table 1.

<Production of pigment water dispersion A>
Production Example A1
The polymer solution (a) obtained in Synthesis Example 1 was dried under reduced pressure, and 25 parts of the polymer obtained was mixed with 78.6 parts of MEK, and 5N aqueous sodium hydroxide solution (solid content of sodium hydroxide 16.9%, sum) 12.7 parts of light pure chemical industry product make, for volume titration) was added, and it neutralized so that the ratio of the number-of-moles of sodium hydroxide to the number-of-moles of the carboxyl group of a polymer might be 50 mol%. %). Further, 400 parts of ion exchange water was added.
Furthermore, 100 parts of cyan pigment (CI pigment blue 15: 3, manufactured by DIC Corporation) is added, and a disper wing is prepared at 20 ° C. using Disper (manufactured by Asada Iron Works Co., Ltd., Ultra Disper: trade name) The mixture was stirred for 60 minutes under conditions of rotation at 7,000 rpm.
The obtained mixture was subjected to 10-pass dispersion treatment with a microfluidizer (manufactured by Microfluidics, trade name) at a pressure of 200 MPa. 250 parts of ion-exchanged water is added to the obtained dispersion, and after stirring, MEK is completely removed at 60 ° C. under reduced pressure, and a part of water is further removed, and a 5 μm filter (acetyl cellulose membrane, outer diameter Pigment aqueous dispersion A1 having a solid content concentration of 20% by filtering with a 25 mL needleless syringe (manufactured by Terumo Corporation) having a volume of 2.5 cm, manufactured by Fujifilm Corporation) and removing coarse particles I got The results are shown in Table 2.

Production Example A2 to A6, Comparative Production Example A1
In Preparation Example A1, the pigment described in Table 2 is used instead of the cyan pigment, and instead of the polymer solution (a), the polymer solution obtained in Preparation Example 2 (b) or the polymer obtained in Preparation Example 3 Solution (c) was dried under reduced pressure, and the resulting polymer was 25 parts. The amount of the 5 N aqueous solution of sodium hydroxide was changed to the amount described in Table 2 to obtain a degree of neutralization of 50 mol%. Pigment water dispersions A2 to A7 were obtained in the same manner as in Example A1. The results are shown in Table 2.
The details of the pigments shown in Table 2 are as follows.
Cyan: C.I. I. Pigment blue 15: 3 (manufactured by DIC Corporation)
Magenta: C.I. I. Pigment red 150 (made by Dainichi Seika Kogyo Co., Ltd.)
Yellow: C.I. I. Pigment yellow 74 (made by Dainichi Seika Kogyo Co., Ltd.)

<Production of Water-based Pigment Dispersion B>
Production Example B1
100 parts (solid content 20%) of the pigment water dispersion A1 obtained in Production Example A1 is taken in a screw cap glass bottle, and trimethylolpropane polyglycidyl is used as a crosslinking agent having three epoxy groups in one molecule. Add ether (Nagase Chemtex Co., Ltd., Denacol EX-321, molecular weight 302, epoxy equivalent 140, water solubility 27%) 1.68 parts (crosslink degree 70%), close tightly, and stir at 70 ° C with a stirrer Heated for 5 hours. After 5 hours, cool to room temperature and filter with a 25 mL needleless syringe (manufactured by Terumo Corp.) equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corp.) Water-based pigment dispersion B1 was obtained.

Production Examples B2 to B10, Comparative Production Examples B1 to B6
Using pigment water dispersions A1 to A7 shown in Table 3, aqueous pigment dispersions B2 to B16 were obtained in the same manner as in Production Example B1, except that the conditions shown in Table 3 were used.

Preparation of water-based ink and ink set and evaluation test
Examples 1 to 4 and Comparative Examples 1 to 8
(1) Preparation of Water-Based Ink Using the water-based pigment dispersions B1 to B16 obtained in Production Examples B1 to B10 and Comparative Production Examples B1 to B6, the pigment concentration is 5% and propylene glycol 20% with respect to the entire water-based ink. Triethylene glycol (Wako Pure Chemical Industries, Ltd., reagent) 5%, Acetylenol E 100 (Kawaken Fine Chemical Co., Ltd., 2,4,7,9-Tetramethyl-5-decyne-4,7-diol ethylene oxide) It was adjusted to 10% adduct) 1%, ion exchange water was added, and the total amount was measured to be 100%. Thereafter, the above components are stirred with a magnetic stirrer and mixed well, and filtered with a 25 mL needleless syringe fitted with a 1.2 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) Thus, cyan, magenta and yellow water-based inks C1 to C16 were obtained.

[Evaluation of water-based ink]
The following test 1 (storage stability evaluation) was performed using the obtained water-based inks C1 to C16. The results are shown in Table 3.
(Test 1: storage stability evaluation)
Each water-based ink is sealed in a screw tube manufactured by Maruem Co., Ltd. and left in a thermostatic chamber set at 60 ° C. for one week, and then the average particle diameter is measured. Calculated. As the particle size increase rate is smaller, the aggregation of pigment particles is suppressed, and the storage stability is excellent.
Average particle size increase rate (%) = [(average particle size of ink after storage−average particle size of water dispersion used for ink preparation) / average particle size of water dispersion used for ink preparation] × 100

(2) Preparation of Ink Set The water-based inks obtained in the above (1) were combined as shown in Table 4 to obtain ink sets 1 to 12.
[Evaluation of ink set]
The following test 2 (color-to-color mixing evaluation) and test 3 (abrasion resistance evaluation) were performed using the obtained ink sets 1 to 12. The results are shown in Table 4.

(Test 2: Evaluation of color mixing between colors)
(A) Preparation of inkjet printed matter A printing evaluation apparatus (stock) equipped with an inkjet recording head "KJ4B-HD06MHG-STDV" (Kyocera Corporation, piezo type) in an environment of temperature 25 ± 1 ° C and relative humidity 30 ± 5% The water-based ink obtained in the example and the comparative example was filled in company Tri-Tek.
A head voltage of 26 V, a frequency of 30 kHz, an appropriate amount of discharge liquid of 12 pl, a head temperature of 32 ° C., a resolution of 600 dpi, a flushing number of 200 before discharge, and a negative pressure of -4.0 kPa were set.
Conveys the recording medium (Gross coated paper “OK Top Coat Plus” (manufactured by Oji Paper Co., Ltd.), A4 size, water absorption amount: 4.9 g / m ² ) in the same direction as the longitudinal direction of the recording medium. It fixed to the stand by decompression.
A print command was transferred to the print evaluation apparatus, and water-based ink was printed on a recording medium by an ink jet recording method to produce various printed materials with a drive amount of 12 pl and 600 × 600 dpi, and the following evaluation test for intercolor color mixture was performed.

(B) Evaluation of intercolor mixing The second ink was solid printed (1C) at 100% duty within 1 second after recording the character “a” with the first ink. Within one second, solid print (2C) the third ink at 100% duty on the area where the second ink was recorded, and when a total of 200% duty is recorded, the character “a” is clearly confirmed The following criteria evaluated whether it could do. The combinations of the first, second and third inks are similarly evaluated for (i) cyan, magenta, yellow, (ii) yellow, magenta, cyan, and (iii) magenta, cyan and yellow, and these three evaluation results The lowest value of was taken as the evaluation value.
(Evaluation criteria)
Evaluation 5: In the 200% Duty portion of the 2C solid printed portion, there is no blur of the “a” printed portion, and characters can be recognized.
Evaluation 4: In the 200% Duty portion of the 2C solid printed portion, the “a” printed portion blurs slightly but characters can be recognized.
Evaluation 3: In the 200% Duty portion of the 2C solid printed portion, the “a” printed portion blurs and a drop in character grade is observed, but characters can be recognized.
Evaluation 2: In the 200% Duty portion of the 2C solid printed portion, the “a” printed portion blurs and a marked deterioration in character quality is observed, but characters can be recognized.
Evaluation: In the 200% Duty portion of the 1: 2 C solid printed portion, the “a” printed portion blurs and characters can not be recognized.

(Test 3: Evaluation of abrasion resistance at 3 C driving)
In 3C solid printing, within 1 second after solid printing (1C) with the first ink, solid ink (2C) with the second ink is superimposed on the portion where the first ink is recorded, and then 1 Within seconds, the area where the second ink was recorded was further superimposed on the area where the second ink was recorded, and solid printing (3C) was performed with the third ink. The solid printing was carried out with the duty of single color set to 70%.
After printing, it is left for 24 hours in an environment of temperature 23 ° C. and humidity 50%, and the obtained printed matter is coated paper as a friction material (Oji Paper Co., Ltd.) using a clock meter (QM-621A manufactured by Imoto Machinery Co., Ltd.) The printed material was subjected to an abrasion test by rubbing (five reciprocations) five times (5 round trips) with a company-made OK top coat).
The print density of the ink transferred to the coated paper used as a friction material after the test was measured by an optical spectrophotometer (SpectroEye, manufactured by Sakata Inx Engineering Co., Ltd.).
The combinations of the first, second and third inks are similarly evaluated for (i) cyan, magenta, yellow, (ii) yellow, magenta, cyan, and (iii) magenta, cyan and yellow, and these three evaluation results The lowest value of was taken as the evaluation value.
The smaller the transfer density, the less the ink transfer and the better the fixability.

  From Tables 3 and 4, the ink set of the example is excellent in the storage stability of the ink as compared to the ink set of the comparative example, and the abrasion resistance is obtained even when using the ink excellent in the storage stability. It can be seen that recorded matter excellent in quality and image quality can be obtained.

Claims (8)

An ink set containing at least inks of respective colors of cyan, yellow and magenta, the ink of each color corresponding to either ink (A) or ink (B) satisfying the following conditions, and An ink set in which all ink does not correspond to ink (A) or all ink does not correspond to ink (B).
Condition of Ink (A) or Ink (B)
The ink (A) and the ink (B) are aqueous inks in which a pigment is dispersed in an aqueous medium with a polymer, and the polymer is obtained by crosslinking a polymer having an acid value of 140 mg KOH / g or more and 260 mg KOH / g or less with a crosslinking agent. Water-insoluble crosslinked polymer
The residual acid value of the water-insoluble crosslinked polymer in the ink (A) is 78 mg KOH / g or more and less than 100 mg KOH / g, and the residual acid value of the water-insoluble crosslinked polymer in the ink (B) is 56 mg KOH / g or more and less than 78 mg KOH / g.   The difference between the residual acid number of the water-insoluble crosslinked polymer in ink (A) and the residual acid number of the water-insoluble crosslinked polymer in ink (B) is 5 mg KOH / g or more and 45 mg KOH / g or less. Ink set.   The ink set according to claim 1, wherein the polymer is a polymer having a carboxy group.   A polymer having a carboxy group is a structural unit derived from at least one carboxy group-containing vinyl monomer selected from acrylic acid and methacrylic acid, and an alkyl group having 1 to 22 carbon atoms or an aryl group having 6 to 22 carbon atoms The ink set according to claim 3, which is a vinyl polymer containing a structural unit derived from at least one hydrophobic monomer selected from an acrylate monomer having a methacrylate monomer, a methacrylate monomer and an aromatic group-containing monomer.   The ink set according to any one of claims 1 to 4, wherein the crosslinking agent is a glycidyl ether compound of polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms.   The ink set according to any one of claims 1 to 5, which is for inkjet recording.   An ink jet recording method for recording on a low liquid absorption recording medium using the ink set according to any one of claims 1 to 6.   The ink jet recording method according to claim 7, wherein the low liquid absorbing recording medium is a coated paper or a resin film.