JP6831313B2 - Water-based ink composition for inkjet recording and image formation method - Google Patents

Description

The present invention relates to a water-based ink composition for inkjet recording and an image forming method.

As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are recording methods such as an electrophotographic method, a sublimation type and a molten type thermal transfer method, and an inkjet method.
The inkjet recording method does not require a printing plate, and ejects ink only to the image forming portion to form an image directly on the recording medium. Therefore, the ink can be used efficiently and the running cost is reduced. Further, in the inkjet recording method, the printing device is relatively low in cost as compared with the conventional printing machine, can be miniaturized, and has less noise. As described above, the inkjet recording method has various advantages as compared with other image recording methods.

Improvements are being made to the ink used in the inkjet recording method that has the above-mentioned advantages. For example, Patent Documents 1 to 4 describe fine particles of a resin containing a constituent component derived from sodium alkylallyl sulfosuccinate and a constituent component derived from styrene, and a water-soluble organic solvent of glycerin, (di) ethylene glycol or ethanol. , Water-based ink compositions containing water are described.

Japanese Unexamined Patent Publication No. 2008-150507 Special Table 2009-535486 JP-A-2002-020656 JP-A-2017-141441

The inkjet recording method has been mainly used in the fields of office printers, home printers, and the like. Furthermore, in recent years, its use has expanded to the commercial printing field, and the image quality and speed of inkjet recording are increasing.
Along with this, the performance required for the ink used in the inkjet recording method is also becoming more sophisticated. For example, in order to cope with high speed, quick-drying (drying property) is required in which the ink after ejection dries quickly. On the other hand, for ink for inkjet recording, ejection (stability) and storage stability that can stably eject a desired amount of ink from a nozzle are also important. Furthermore, the ink is also required to be able to form an image showing high mechanical strength (rubbing resistance) that is not damaged or peeled off even when an external force is applied, with high image quality.
Moreover, in the ink composition for inkjet recording, even if the pigments and resin fine particles of the components are finely dispersed at the time of manufacture, the finely divided components may reaggregate or gel, which results in image quality and ejection property. The reaggregates or gels are usually removed using a fine filter (for example, a mesh or a pore size of about 2 to 5 μm). However, conventional inks have not been able to sufficiently suppress reaggregation or gelation of compositions containing micronizing components. Therefore, clogging is likely to occur in the filtration process, and the image quality is deteriorated. From the viewpoint of industrial production (manufacturing suitability), high image quality of images, and maintenance of ejection properties, inks for inkjet recording are subject to reaggregation or gelation of micronized components not only after production but also during production. There is a need to develop an ink composition that suppresses and retains filterability (dispersion stability).

The present invention exhibits high storage stability and excellent filterability for a fine filter, and when applied to an inkjet recording method, forms an image having excellent ejection properties and drying properties, as well as excellent image quality and abrasion resistance. An object of the present invention is to provide a water-based ink composition for inkjet recording that can be used, and an image forming method using the water-based ink composition for inkjet recording.

As a result of diligent studies in view of the above problems, the present inventors have found that fine particles of a resin having a specific structural unit (repeating unit) having a long-chain alkyl group and a structural unit having a specific ring structure, and specific fine particles of a resin. It has been found that an aqueous ink composition used in combination with a hydrophobic organic solvent exhibits high storage stability and can suppress aggregation of fine particles and the like. Moreover, it has been found that when this water-based ink composition is used as an ink for an inkjet recording method, it is excellent in ejection property and drying property, and further, when this water-based ink composition is used, an image excellent in image quality and abrasion resistance can be formed. It was. The present invention has been further studied based on these findings and has been completed.

一般式（Ｉ）中、Ｒは炭素数７〜３０のアルキレン基を示す。Ｌ^１ は単結合、＊＊−アルキレン基−Ｃ（＝Ｏ）−Ｏ−基又は＊＊−アリーレン基−Ｃ（＝Ｏ）−Ｏ−基を示す。ここで、＊＊は一般式（Ｉ）中のカルボニル炭素原子との連結部を示す。Ｒ及びＬ ^１ は、置換基として、シクロアルキル、芳香族炭化水素環基、芳香族ヘテロ環基、ＳＯ _３ Ｍ又はＣＯＯＭを有していてもよい。Ｌ ^２ は単結合を示す。Ｌ^３は水素原子、ＳＯ_３Ｍ又はＣＯＯＭを示す。Ｍはアルカリ金属イオン又はアンモニウムイオンを示す。ただし、Ｒ、Ｌ^１及びＬ^３の少なくとも１つはＳＯ_３Ｍ又はＣＯＯＭを有する。

一般式（Ａ）〜（Ｅ）中、Ｒ^１１及びＲ^１２はメチル又は水素原子を示す。Ｒ^１３は炭素数１〜１０の直鎖状若しくは分岐鎖状のアルキル基を示す。一般式（Ａ）及び一般式（Ｂ）中のｎは０〜５の整数であり、一般式（Ｃ）中のｎは０〜１１の整数である。Ｌ^１１は単結合、炭素数１〜１８の直鎖状、分岐鎖状若しくは環状のアルキレン基、炭素数６〜１８のアリーレン基、−Ｏ−、−ＮＨ−、−Ｓ−若しくは−Ｃ（＝Ｏ）−、又は、これらを２個以上連結して形成される２価の連結基を示す。 The above-mentioned problems of the present invention have been solved by the following means.
<1> A water-based ink composition for inkjet recording, which contains water, an organic solvent, and resin fine particles.
The organic solvent contains an alcohol solvent as a hydrophobic organic solvent (d1) having a ClogP value of 0 to 3.5 and an organic solvent (dr1) having a ClogP value of −3.0 or more and less than 0 .
The content of the hydrophobic organic solvent (d1) in the aqueous ink composition for inkjet recording is 0.5 to 10% by mass, and the total content of the hydrophobic organic solvent (d1) and the organic solvent (dr1) is 6-40% by mass,
The fine resin particles has 3-20 mass% of structural units represented by the following general formula (I) in the resin particles, and a structural unit represented by any one of the following general formula (A) ~ (E) A water-based ink composition for inkjet recording.

In the general formula (I), R represents an alkylene group having 7 to 30 carbon atoms. L ¹ represents a single bond , **-alkylene group-C (= O) -O- group or **-arylene group-C (= O) -O- group. Here, ** indicates a connecting portion with a carbonyl carbon atom in the general formula (I) . R and L ¹ may have a cycloalkyl, an aromatic hydrocarbon ring group, an aromatic heterocyclic group, SO ₃ M or COOM as a substituent . L ² indicates a single bond. L ³ is shows the hydrogen atom, SO ₃ M or COOM. M represents an alkali metal ion or an ammonium ion. However, at least one of R, L ¹ and L ³ has SO ₃ M or COOM.

In the general formulas (A) to (E), R ¹¹ and R ¹² represent a methyl or hydrogen atom. R ¹³ represents a linear or branched alkyl group having 1 to 10 carbon atoms. N in the general formula (A) and the general formula (B) is an integer of 0 to 5, and n in the general formula (C) is an integer of 0 to 11. L ¹¹ is a single bond, a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- or -C (=). O)-or a divalent linking group formed by linking two or more of these.

<2> The water-based ink composition for inkjet recording according to <1> , wherein the content of the structural unit represented by the general formula (A) in the resin fine particles is 5 to 50% by mass.
<3> The water-based ink composition for inkjet recording according to <1> or <2> , wherein at least one of R, L ¹ and L ³ of the general formula (I) has SO ₃ M.
<4> The aqueous ink composition for inkjet recording according to any one of <1> to <3>, wherein the organic solvent (dr1) contains diethylene glycol, dipropylene glycol, propylene glycol or 1,2-butanediol.
<5> The method according to any one of <1> to <4>, wherein the content ratio (mass basis) of the hydrophobic organic solvent (d1) to the organic solvent (dr1) is 1: 1 to 1:30. Aqueous ink composition for inkjet recording.
<6> The aqueous ink composition for inkjet recording according to any one of <1> to <5>, which contains a pigment.
<7> An image forming method including an ink applying step of applying the water-based ink composition for inkjet recording according to <6> above onto a recording medium by an inkjet method to form an image.
<8> The image forming method according to <7>, wherein the water-based ink composition for inkjet recording is directly applied onto a low-water-absorbing recording medium or a non-water-absorbent recording medium.

In the present specification, unless otherwise specified, when there are a plurality of substituents, linking groups, ligands, structural units, etc. (hereinafter referred to as substituents, etc.) represented by specific codes, or a plurality of substituents, etc. Are specified simultaneously or alternately, and the substituents and the like may be the same or different from each other. This also applies to the regulation of the number of substituents and the like.
In the present specification, the "group" of each group described as an example of each substituent is used to mean that it includes both an unsubstituted form and a form having a substituent. For example, "alkyl group" means an alkyl group which may have a substituent.
As used herein, the term "(meth) acrylate" is used to include both acrylate and methacrylate. This also applies to "(meth) acrylic acid", "(meth) acrylamide" and "(meth) acryloyl group".
The numerical range represented by using "~" in the present specification means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

The aqueous ink composition for inkjet recording of the present invention exhibits high storage stability and dispersion stability (excellent filterability for a fine filter). Moreover, this water-based ink composition for inkjet recording can form an image having excellent ejection properties and drying properties, and further excellent image quality and abrasion resistance when applied to an inkjet recording method. The image forming method of the present invention can stably form an image having excellent image quality and abrasion resistance by using the aqueous ink composition for inkjet recording of the present invention exhibiting the above-mentioned excellent characteristics.

The water-based ink composition for inkjet recording of the present invention (hereinafter, may be simply referred to as the water-based ink composition of the present invention), the image forming method, and preferred embodiments of the resin fine particles will be described below.

[Aqueous ink composition for inkjet recording]
The water-based ink composition of the present invention contains water, an organic solvent, and specific resin fine particles. In addition, the water-based ink composition of the present invention usually contains a pigment. When the water-based ink composition of the present invention does not contain a pigment, it can be used as a clear ink, and when it contains a pigment, it can be used for color image forming applications.
The reason why the water-based ink composition of the present invention containing the above components exhibits the above-mentioned excellent action and effect is not clear, but it is considered as follows.
This water-based ink composition contains resin fine particles having a structural unit (I) and a structural unit (II), which will be described later, and a specific amount of a hydrophobic organic solvent. When the resin fine particles and the hydrophobic organic solvent coexist, it is considered that the resin fine particles and the hydrophobic organic solvent are expressed in a well-balanced manner without impairing the function and function of each, and the function and function of each are not shown by themselves.
The resin fine particles are composed of a resin having a specific structural unit (I) having a long-chain alkyl group, and the structural unit (I) is contained in a mixed solvent of water and an organic solvent containing a hydrophobic solvent. It functions as an excellent self-emulsifier and can highly disperse the resin fine particles in this mixed solvent (suppress the aggregation or gelation of the resin fine particles). In particular, even if water and / or an organic solvent volatilizes and the content of the resin fine particles increases, excellent dispersibility can be maintained. Moreover, the reaggregation or gelation of the resin fine particles finely dispersed in the water-based ink composition can be effectively suppressed due to the high dispersion stability. Therefore, the water-based ink composition exhibits high storage stability, ejection property and filterability. If water and / or organic solvent is easily volatilized, it contributes to drying property.
Moreover, since the film-forming property is high and the amount of free surfactant is small, the water-based ink composition of the present invention can form a high-quality image with high abrasion resistance when used in an inkjet recording method.

<Water>
As the water used in the present invention, it is preferable to use water that does not contain ionic impurities such as ion-exchanged water and distilled water. The water content in the water-based ink composition is appropriately selected depending on the intended purpose, but is usually preferably 10 to 95% by mass, more preferably 30 to 90% by mass, and 50 to 50 to 90% by mass. It is more preferably 80% by mass.

<Organic solvent>
The organic solvent used in the present invention contains a hydrophobic organic solvent (d1) having a ClogP value of 0.5 to 3.5, and preferably contains an organic solvent (dr1) other than this hydrophobic organic solvent.

− Hydrophobic organic solvent (d1) −
The hydrophobic organic solvent (d1) has a ClogP value of 0.5 to 3.5. When the ClogP value is within this range, the filterability of the water-based ink composition, the dryness when applied to the inkjet recording method, and the image quality of the formed image can be improved. The ClogP value of the hydrophobic organic solvent (d1) is preferably 1.0 or more, and more preferably 1.5 or more, in terms of dryness. On the other hand, in terms of filterability and image quality, it is preferably 3.0 or less, and more preferably 2.7 or less.
In the present invention, the ClogP value of the hydrophobic organic solvent (d1) adopts the value calculated by using ChemBioDrawUltra 13.0.

The hydrophobic organic solvent (d1) is preferably an organic solvent represented by the following formula 1 or formula 2.

In formula 1 or 2, R ¹ represents a hydrogen atom or a methyl group, and R ² is a linear or branched aliphatic hydrocarbon group having 4 to 9 carbon atoms or an aromatic having 6 to 10 carbon atoms. Indicates a hydrocarbon group. n represents an integer of 1 to 3.

In the formula 1, R ¹ is preferably a hydrogen atom from the viewpoint of reducing the surface tension of the ink.
The aliphatic hydrocarbon group that can be taken as R ² is a linear or branched aliphatic hydrocarbon group having 4 to 9 carbon atoms from the viewpoint of setting the ClogP value to 0.5 to 3.5. , A linear or branched aliphatic hydrocarbon group having 6 to 8 carbon atoms is preferable. The alkyl group is preferable as the aliphatic hydrocarbon group. The aromatic hydrocarbon group that can be taken as R ² is not particularly limited, but a phenyl group or a naphthyl group is preferable, and a phenyl group is more preferable.
n is preferably 1 or 2, and more preferably 1 from the viewpoint of reducing the surface tension of the ink.
In formula 2, R ² has the same meaning as R ² in formula 1, and the preferred one is also the same.
The hydrophobic organic solvent (d1) is preferably the organic solvent represented by the formula 1 from the viewpoint of filterability, dryness and image quality, and the organic solvent represented by the formula 2 from the viewpoint of ink storage stability. preferable.

Preferred hydrophobic organic solvents (d1) include, for example, ethylene glycol mono (C4 to C9) alkyl ether, diethylene glycol mono (C4 to C9) alkyl ether, triethylene glycol mono (C4 to C9) alkyl ether, and propylene glycol mono ( Examples thereof include C4 to C9) alkyl ethers, dipropylene glycol mono (C4 to C9) alkyl ethers, tripropylene glycol mono (C4 to C9) alkyl ethers, and other alcohols.

Examples of the ethylene glycol mono (C4 to C9) alkyl ether include ethylene glycol monobutyl ether, ethylene glycol monopentyl ether, ethylene glycol monohexyl ether, ethylene glycol monoheptyl ether, ethylene glycol monooctyl ether, and ethylene glycol monononyl ether. Ethylene glycol mono-2-ethylhexyl ether can be mentioned.
Examples of the diethylene glycol mono (C4-C9) alkyl ether include diethylene glycol monobutyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, diethylene glycol monoheptyl ether, diethylene glycol monooctyl ether, diethylene glycol monononyl ether, and diethylene glycol mono-2-ethylhexyl ether. Can be mentioned.
Examples of the triethylene glycol mono (C4 to C9) alkyl ether include triethylene glycol monobutyl ether, triethylene glycol monopentyl ether, triethylene glycol monohexyl ether, triethylene glycol monoheptyl ether, and triethylene glycol monooctyl ether. Examples thereof include triethylene glycol monononyl ether and triethylene glycol mono-2-ethylhexyl ether.

Examples of the propylene glycol mono (C4 to C9) alkyl ether include propylene glycol monobutyl ether, propylene glycol monopentyl ether, propylene glycol monohexyl ether, propylene glycol monoheptyl ether, propylene glycol monooctyl ether, and propylene glycol mono-2-. Ethylhexyl ether can be mentioned.
Examples of the dipropylene glycol mono (C4 to C9) alkyl ether include dipropylene glycol monobutyl ether, dipropylene glycol monopentyl ether, dipropylene glycol monohexyl ether, dipropylene glycol monoheptyl ether, and dipropylene glycol monooctyl ether. Dipropylene glycol mono-2-ethylhexyl ether can be mentioned.
Examples of the tripropylene glycol mono (C4 to C9) alkyl ether include tripropylene glycol monobutyl ether, tripropylene glycol monopentyl ether, tripropylene glycol monohexyl ether, tripropylene glycol monoheptyl ether, and tripropylene glycol monooctyl ether. Examples thereof include tripropylene glycol mono-2-ethylhexyl ether.

Examples of other alcohols include 1,2-hexanediol, 1,2-heptandiol, 1,2-octanediol, 1,2-nonanediol, 1,2-decanediol, and examples described later. Examples thereof include the alcohol solvents (d1-1) to) d1-8) used.

Of these, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, diethylene glycol mono-2-ethylhexyl ether, and 1,2-octanediol are preferable.

The hydrophobic organic solvent (d1) can be used alone or in combination of two or more.

-Organic solvent (dr1)-
The organic solvent (dr1) may be any organic solvent other than the hydrophobic organic solvent (d1), and from the viewpoint of drying property, the vapor pressure at 20 ° C. is preferably 1.0 Pa or more. In the present invention, even if the vapor pressure at 20 ° C. is 1.0 Pa or more, the solvent corresponding to the hydrophobic organic solvent (d1) does not correspond to the organic solvent (dr1).
The vapor pressure of the organic solvent (dr1) is preferably 1.0 Pa or more, more preferably 2.0 Pa or more, and further preferably 10 Pa or more at 20 ° C.
The vapor pressure of the organic solvent (dr1) is measured by a known method, and can be determined by, for example, a static method (measurement temperature 20 ° C.). Vapor pressure measurement by the static method is a method of directly or indirectly measuring the pressure of vapor in equilibrium with a solid of a sample, and is measured according to OECD Guideline 104.

The ClogP value of the organic solvent (dr1) is preferably smaller than the ClogP value of the monomer unit c-1 from the viewpoint of ejection property.
The ClogP value of the organic solvent (dr1) (the measurement method is as described above) is preferably −3.0 or more and less than 0, and more preferably −0.2 or more and less than 0.

The organic solvent (dr1) is not particularly limited, but for example, diethylene glycol (vapor pressure at 20 ° C.: 2.7 Pa, ClogP value: -1.30), dipropylene glycol (DPG, vapor pressure at 20 ° C.: 1. 3Pa, ClogP value: -0.69), propylene glycol (PG, vapor pressure at 20 ° C.: 10.6Pa, ClogP value: -1.06), and 1,2-butanediol (vapor pressure at 20 ° C.: 2). .7 Pa, ClogP value: -0.53) and the like. Of these, propylene glycol or dipropylene glycol is preferable from the viewpoint of dryness.

The organic solvent (dr1) can be used alone or in combination of two or more.

The content of the organic solvent in the aqueous ink composition of the present invention is 6 to 40% by mass in total of the hydrophobic organic solvent (d1) and the organic solvent (dr1) from the viewpoint of ejection property and drying property. It is more preferable, it is more preferably 10 to 30% by mass, and further preferably 15 to 25% by mass.
The content of the hydrophobic organic solvent (d1) in the aqueous ink composition of the present invention is 0.5 to 10% by mass. When the content of the hydrophobic organic solvent (d1) is within the above range, it is easy to prepare an aqueous ink composition having a uniform composition, and the storage stability, drying property and image quality are excellent. This content is preferably 1.0% by mass or more from the viewpoint of dryness, and preferably 5.0% by mass or less from the viewpoint of storage stability and image quality.
The content of the organic solvent (dr1) in the aqueous ink composition of the present invention is preferably 1 to 40% by mass, preferably 5 to 30% by mass, from the viewpoint of ejection property and dryness. , 10 to 25% by mass, more preferably.
In the aqueous ink composition of the present invention, the content ratio (mass basis) of the hydrophobic organic solvent (d1) to the organic solvent (dr1) is determined from the viewpoint of ejection property and drying property, and the hydrophobic organic solvent (d1): The organic solvent (dr1) is preferably 1: 1 to 1:30, more preferably 1: 2 to 1:20, and even more preferably 1: 3 to 1:15.

<Resin fine particles>
The resin fine particles (resin constituting the resin fine particles) used in the present invention are represented by the structural unit (I) represented by the following general formula (I) and any of the following general formulas (A) to (E). It has a structural unit (II). By using the resin fine particles as a dispersion in combination with the hydrophobic organic solvent (d1), the above-mentioned excellent properties can be imparted to the aqueous ink composition of the present invention.
The structural unit (I) and the structural unit (II) contained in the resin fine particles may be one type or two or more types, respectively. The resin fine particles preferably have a structural unit other than the structural unit (I) and the structural unit (II).

The structural units that form the resin fine particles will be specifically described below.
− Structural unit (I) −
The structural unit (I) is represented by the following formula (1).

In the formula (1), R represents an alkylene group having 7 or more carbon atoms. The alkylene group has preferably 8 or more carbon atoms, more preferably 10 or more carbon atoms, and further preferably 12 or more carbon atoms. On the other hand, the upper limit of the number of carbon atoms is not particularly limited, but is, for example, preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less.
Here, the number of carbon atoms of the alkylene group that can be taken as R is determined so that the number of carbon atoms is the largest in the −L ¹ −RL ² − chain including L ¹ and L ² described later. That is, among the linking groups that can be taken as L ¹ and L ² , the linking group that directly bonds to R does not take an alkylene group.
For example, the structural unit (c1-4) shown in Examples described later has an alkyl group having 14 carbon atoms as a −L ¹ −RL ² − chain. In this case, both L ¹ and L ² which are divalent linking groups can be interpreted as alkylene groups. However, in the present invention, when determining the number of carbon atoms of the alkylene group R as above, but L ¹ and L ² are both single bonds, R is interpreted as an alkylene group having 14 carbon atoms (Hekisadekaniren group).

The alkylene group that can be taken as R may be linear, branched or cyclic, but is preferably linear or branched, and more preferably linear.
R may have a substituent. Examples of such substituents is not particularly limited, for example, (cyclo) alkyl group, an aromatic hydrocarbon ring group, aromatic heterocyclic group, include SO 3 _M or COOM, etc. will be described later.

L ¹ and L ² represent a single bond or a divalent linking group, respectively.
The linking group that can be taken as L ¹ and L ² is not particularly limited, and for example, an alkylene group, an arylene group, -O-, -NH-, -S- or -C (= O)-, or 2 of these. Examples thereof include a linking group formed by linking one or more groups. The number of groups to be linked is not particularly limited as long as it is 2 or more, and for example, 2 to 7 is preferable, and 2 to 5 is more preferable. At this time, the alkylene group having the longest molecular chain is used as one linking group. That is, in the case of a propylene group, it is counted as one alkylene group and not as three methylene groups.

The alkylene group that can be taken as L ¹ and L ² may be linear, branched chain, or cyclic, but is preferably linear or branched chain, and is preferably linear. More preferred. The carbon number of the alkylene group is preferably 1 to 8, more preferably 1 to 6, further preferably 1 to 3, and particularly preferably 2.
The arylene group that can be taken as L ¹ and L ² may be a monocyclic ring or a condensed ring, and may be an aromatic hydrocarbon ring group or an aromatic heterocyclic group. The carbon number of the arylene group is not particularly limited, but is preferably 6 to 22, more preferably 6 to 18, and even more preferably 6 to 10. Examples of the arylene group include a phenylene group, a naphthylene group, an anthranyl group and the like.

The linking group that can be taken as L ¹ is preferably * -alkylene group-C (= O) -O- group, * -allylen group-C (= O) -O- group, and * -alkylene group-C (= O). ) -O- group is more preferable.
The linking groups that can be taken as L ² are * -OC (= O) -group, * -C (= O) -O- group, * -NH-C (= O) -group, and * -C (=). O) -NH- group, * -C (= O) -O-alkylene group, * -C (= O) -O-arylene group, * -O- group, * -C (= O) -group, * -O-C (= O) -O- group, * -O-N (= O) -O- group is preferable, * -OC (= O) -group, * -C (= O) -O -Group, * -NH-C (= O) -group are more preferable.
In the above linking group, * indicates a linking portion with a carbonyl carbon atom in the general formula.

L ¹ and L ² may each have a substituent. Such a substituent is not particularly limited, and has the same meaning as the substituent that R may have, and the preferred one is also the same.
As L ¹ , a divalent linking group containing SO ₃ M (excluding the alkylene group when it is one linking group) is preferable, and a divalent linking group containing SO ₃ M (alkylene group, arylene group) is preferable. Alternatively, a linking group formed by linking two or more groups containing -NH-) is more preferable, and an alkylene group containing SO ₃ M and a -C (= O) -O- group are linked and formed. Linking groups are more preferred.

L ³ represents a hydrogen atom, SO ₃ M or COOM, preferably a hydrogen atom or SO ₃ M, and more preferably a hydrogen atom. M represents an alkali metal ion or an ammonium ion. From the viewpoint of discharge stability, latency and stability of the resin fine particles, M is preferably an alkali metal ion, more preferably sodium ion or potassium ion, and even more preferably sodium ion. In the water-based ink composition of the present invention, M may be dissociated (free).

The structural unit (I) has at least one of R, L ¹ and L ³ having SO ₃ M or COOM. That is, when L ³ adopts a hydrogen atom, at least ^one of R and L ¹ has SO ₃ M or COOM as a substituent. In the present invention, it is preferable that L ³ takes a hydrogen atom and L ¹ has SO ₃ M or COOM as a substituent.
The number of SO ₃ M and COOM contained in the structural unit (I) may be at least one, and is preferably 1 to 3, for example.

Specific examples of the structural unit (I) include those shown in the Examples column, but the present invention is not limited thereto.

− Structural unit (II) −
The resin fine particles (resin forming the resin fine particles) contain a structural unit (II) of an ethylenically unsaturated compound having an aromatic ring or an aliphatic ring.
Examples of the aromatic ring or aliphatic ring contained in the structural unit (II) include a benzene ring, a naphthalene ring, an anthracene ring, and an aliphatic hydrocarbon ring having 5 to 20 carbon atoms, and the benzene ring and carbon. An aliphatic hydrocarbon ring having a number of 6 to 10 is preferable.
These aromatic rings or aliphatic rings may have a substituent. When the aromatic ring or the aliphatic ring has a substituent, the substituent is not particularly limited, include substituents other than the SO 3 _M and COOM.

As the ethylenically unsaturated compound having an aromatic ring or an aliphatic ring leading to the structural unit (II), an ethylenically unsaturated compound having an ethylenically unsaturated group at the end of the compound is preferable, and styrene or (meth) acrylate The compound or (meth) acrylamide compound is more preferable, and the styrene or (meth) acrylate compound which may have a substituent is further preferable.
The ethylenically unsaturated compound is not particularly limited, and examples thereof include compounds that derive structural units represented by any of the following general formulas (A) to (E), and more specifically, styrene. , Benzyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate and the like.

The structural unit (II) preferably includes a structural unit represented by any one of the following general formulas (A) to (E) from the viewpoint of manufacturing suitability (filterability) of the obtained image. From the viewpoint of the stability of particles in the ink, it is more preferable to include the structural unit represented by the following general formula (A).

In the general formulas (A) to (E), R ¹¹ and R ¹² each independently represent a methyl group or a hydrogen atom. Each of R ¹³ independently represents a linear or branched-chain alkyl group having 1 to 10 carbon atoms. In the general formula (A) and the general formula (B), n represents an integer of 0 to 5. N in the general formula (C) is an integer from 0 to 11. L ¹¹ is a single bond, a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- or -C ( = O) −, or a divalent linking group formed by linking two or more of these.

In the general formula (A), R ¹¹ is preferably a hydrogen atom.
In the general formulas (B) to (E), R ¹² is preferably a methyl group.
In the general formulas (A) to (C), R ¹³ is preferably a linear or branched alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group or an ethyl group. When the structural unit represented by each equation has a plurality of R ¹³ , they may be combined with each other to form a ring. However, in the structural unit represented by the general formula (C), when a plurality of R ¹³ are bonded to each other to form a ring, the structural unit is not represented by the general formulas (D) and (E). ..
In any of the formulas, n is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

In the general formula (B), L ¹¹ is preferably a divalent linking group containing -O- or -NH- at the bonding site between the carbonyl group and the bonded carbon atom described in the general formula (B). A divalent linking group containing -O- or -NH- at the bonding site with the carbon atom bonded to the carbonyl group and containing a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms. Is more preferable, −OCH ₂ − or −NHCH ₂ − is further preferable, and −OCH ₂ − is particularly preferable.
In the general formulas (C) to (E), L ¹¹ has -O- or-at the binding site between the carbonyl group and the carbon atom bonded to the carbonyl group described in the general formulas (C) to (E). A divalent linking group containing NH- is preferable, -O- or -NH- is more preferable, and -O- is even more preferable.

The structural unit represented by the general formula (A) is preferably a structural unit derived from styrene.
The structural unit represented by the general formula (B) is preferably a structural unit derived from benzyl (meth) acrylate.
The structural unit represented by the general formula (C) is preferably a structural unit derived from cyclohexyl (meth) acrylate.
The structural unit represented by the general formula (D) is preferably a structural unit derived from isobornyl (meth) acrylate.
The structural unit represented by the general formula (E) is preferably a structural unit derived from dicyclopentanyl (meth) acrylate.

Specific examples of the structural unit (II) include those used in Examples, but the present invention is not limited thereto.

− Other structural units (III) −
The resin fine particles may have a structural unit (referred to as "another structural unit (III)") other than the structural unit (I) and the structural unit (II).
The other structural unit (III) is not particularly limited as long as it is derived from a compound that can be polymerized with the structural unit (I) or (II), and suitable examples thereof include JP-A-2001-181549 and JP-A-2001-181549. Examples of structural units described in JP-A-2002-88294 can be mentioned.
The other structural unit (III) is preferably a structural unit derived from a (meth) acrylamide compound or a (meth) acrylate compound, and more preferably a structural unit derived from a (meth) acrylate compound.

The other structural unit (III) is a structural unit derived from a (meth) acrylic acid-based compound or a salt thereof (including the above-mentioned alkali metal ion salt or ammonium ion salt), and the alkyl group has 1 to 1 carbon atoms. The structural unit derived from the alkyl (meth) acrylate compound, which is 18, or the structural unit derived from the alkyl (meth) acrylamide compound is preferable, and the structural unit derived from the alkyl (meth) acrylate compound is more preferable. The alkyl (meth) acrylate compound is more preferably an alkyl (meth) acrylate compound having an alkyl group having 1 to 10 carbon atoms.
The alkyl group of the other structural unit (III) may be linear or branched, and has a cyclic structure (excluding those included in the general formulas (C) to (E)). May have.
The other structural unit (III) may have a substituent. As the structural unit substituent which may be possessed by, but are not limited to, the SO 3 _M and substituents other than COOM, for example, a hydroxyl group, and amino group.

The resin fine particles may have one or more other structural units (III).

Specific examples of the structural unit (III) include those used in Examples, but the present invention is not limited thereto.

The resin fine particles have a structural unit (I) and a structural unit (II), preferably a structural unit (III) in an appropriate combination. This combination is not particularly limited, but it is preferable to combine preferable ones of each structural unit.

The content of the structural unit forming the resin fine particles is appropriately determined in consideration of the type and content of other structural units.

The content of the structural unit (I) in the resin fine particles is preferably 1 to 25% by mass. When the content of the structural unit (I) is within the above range, each of the above characteristics, particularly scratch resistance and image quality, can be combined at a high level. From the viewpoint of having each of the above characteristics at a high level and in a well-balanced manner, the content of the structural unit (I) is more preferably 3 to 20 in the resin fine particles, further preferably 5 to 15% by mass, 8 ~ 12% by mass is particularly preferable. When the resin fine particles contain a plurality of types of structural units (I), the content of the structural unit (I) is the total of the contents of each structural unit.

The content of the structural unit (II) in the resin fine particles is preferably 1 to 90% by mass, preferably 5 to 50% by mass, from the viewpoint of storage stability, ejection property, abrasion resistance and filterability. More preferably, 10 to 30% by mass is further preferable. When the resin fine particles contain a plurality of types of structural units (II), the content of the structural unit (II) is the total of the contents of each structural unit.
The content of the structural unit represented by the general formula (A) in the structural unit (II) in the resin fine particles is preferably 5 to 50% by mass, preferably 8 to 40% by mass, from the viewpoint of storage stability and abrasion resistance. The mass% is more preferable, and 10 to 30% by mass is further preferable. When the resin fine particles have a plurality of types of structural units represented by the general formula (A), the above content is the total content of each structural unit.

The content of the other structural unit (III) in the resin fine particles is preferably 0 to 90% by mass, more preferably 0 to 70% by mass, from the viewpoint of ejection property and abrasion resistance. When the resin fine particles contain a plurality of types of structural units (III), the above content is the total content of each structural unit.

In the present invention, the resin fine particles contain the structural units (I) and (II), preferably (III), and the total content of these structural units is preferably 100% by mass.
When the resin fine particles have structural units other than the structural units (I) to (III), the content of the structural units other than the structural units (I) to (III) is 0 to 20% by mass in the resin fine particles. Preferably, 0 to 15% by mass is more preferable, and 0 to 10% by mass is further preferable.

The resin constituting the resin fine particles used in the present invention may be polymerized by any polymerization mode such as a block copolymer, a random copolymer, a graft copolymer, and an alternating copolymer.

The glass transition temperature of the resin fine particles used in the present invention is preferably 30 ° C. to 150 ° C., more preferably 50 ° C. to 130 ° C., still more preferably 70 ° C. to 110 ° C. from the viewpoint of scratch resistance of the obtained image.
In the present invention, the measured Tg obtained by actual measurement is applied to the glass transition temperature. The measurement Tg is the temperature at which the baseline begins to change due to the glass transition when measured at a temperature rise rate of 5 ° C./min using a differential scanning calorimeter (DSC) EXSTAR6220 manufactured by SII Nanotechnology. It is measured as the average of the temperature back to baseline.
However, if measurement is difficult due to decomposition of the resin, sensitivity, etc., the calculated Tg calculated by the following formula is applied. The calculation Tg is calculated by the following formula.

1 / Tg = Σ (X _i / Tg _i )

Here, it is assumed that the resin to be calculated is copolymerized with n kinds of monomers from i = 1 to n. X _i is the mass fraction of the i th monomer component (.SIGMA.X _i = 1), a Tg _i is the i-th glass transition temperature of the homopolymer of monomer (absolute temperature). However, Σ is the sum of i = 1 to n. The value of the glass transition temperature of the homopolymer of each monomer (Tg _i) employs a value of Polymer Handbook (3rd Edition) (J.Brandrup , E.H.Immergut al (Wiley-Interscience, 1989)) ..

The weight average molecular weight (Mw) of the resin constituting the resin fine particles used in the present invention is preferably 10,000 to 1,000,000, and more preferably 20,000 to 500,000. The weight average molecular weight can be measured by a known method using gel permeation chromatography (GPC). HLC-8220GPC (manufactured by Tosoh Corporation) was used as the GPC, and three columns were connected in series using TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, and TSKgel SuperHZ2000 (all trade names manufactured by Tosoh Corporation). THF (tetrahydrofuran) is used as the eluent. The conditions are as follows: the sample concentration is 0.45% by mass, the flow rate is 0.35 ml / min, the sample injection amount is 10 μL, the measurement temperature is 40 ° C., and a differential refractive index detector is used. The calibration curve is "Standard sample TSK standard, polystyrene" manufactured by Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", It is prepared from 8 samples of "A-2500", "A-1000" and "n-propylbenzene".

In the aqueous ink composition of the present invention, the particle size of the resin fine particles is preferably 1 to 200 nm, more preferably 5 to 100 nm, and preferably 10 to 60 nm from the viewpoint of ink ejection property. More preferred.
The particle size of the resin fine particles means a volume average particle size. This volume average particle size is measured by a particle size distribution measuring device using light scattering (for example, Microtrac UPA (registered trademark) EX150 manufactured by Nikkiso Co., Ltd.).

As a method for producing resin particles, a known method can be applied without particular limitation. The resin fine particles are preferably prepared by an emulsification polymerization method. The emulsion polymerization method is a method for preparing resin fine particles by polymerizing an emulsion prepared by adding a monomer, a polymerization initiator, an emulsifier, and a chain transfer agent as necessary in an aqueous medium (for example, water). Is. When this emulsification polymerization method is applied to the preparation of resin fine particles used in the present invention, the monomer leading to the structural unit (I) also functions as an emulsifier. Therefore, it is not necessary to separately mix an emulsifier other than this monomer, but an emulsifier in a public place may be added separately as long as the discharge stability is not deteriorated. Examples of the emulsifier include surfactants (anionic surfactants, nonionic surfactants and cationic surfactants) described later, which may be contained in the aqueous ink composition of the present invention.

The above-mentioned polymerization initiator is not particularly limited, and is not particularly limited, and is an inorganic persulfate (for example, potassium persulfate, sodium persulfate, ammonium persulfate, etc.) and an azo-based initiator (for example, 2,2'-azobis (2-amidinopropane). ) Dihydrochloride, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 4,4'-azobis (4-cyanovaleric acid)), organic peroxide (eg, Peroxypivalate-t-butyl, t-butylhydroperoxide, disuccinate peroxide) and the like, or salts thereof can be used. These can be used alone or in combination of two or more. Of these, it is preferable to use an azo-based initiator or an inorganic peroxide.
The amount of the polymerization initiator used in the present invention is preferably 0.01 to 2 parts by mass, more preferably 0.2 to 1 part by mass, based on 100 parts by mass of all the monomers.

As the chain transfer agent, known compounds such as carbon tetrahalogenates, dimers of styrenes, dimers of (meth) acrylic acid esters, mercaptans, and sulfides can be used. Among them, styrene dimers or mercaptans described in JP-A-5-17510 can be preferably used.

The resin fine particles used in the present invention are preferably dispersed in the above-mentioned aqueous medium. The resin fine particles used in the present invention are more preferably self-dispersing resin fine particles.
In the present invention, the self-dispersible resin fine particles refer to fine particles made of a water-insoluble resin that can be dispersed in an aqueous medium due to the functional groups (particularly SO ₃ M or COOM) of the resin itself. The dispersed state is both an emulsified state (emulsion) in which a water-insoluble resin is dispersed in a liquid state in an aqueous medium and a dispersed state (suspension) in which a water-insoluble resin is dispersed in a solid state in an aqueous medium. Is included. “Water insoluble” means that the amount dissolved in 100 parts by mass (25 ° C.) of water is 5.0 parts by mass or less.
The resin fine particles used in the present invention do not function as a dispersant for pigments, and therefore do not contain pigments inside the particles.

The resin fine particles of the present invention preferably exist in a form dispersed in a mixed solvent of water and an organic solvent.
The content of the resin fine particles in the aqueous ink composition of the present invention is preferably 1 to 20% by mass, more preferably 1 to 10% by mass, from the viewpoint of storage stability and abrasion resistance. It is more preferably 2 to 10% by mass.

<Pigment>
The water-based ink composition of the present invention preferably has a form in which one or more pigments are dispersed.
The type of pigment used in the aqueous ink composition of the present invention is not particularly limited, and ordinary organic or inorganic pigments can be used.
Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments or polycyclic pigments are preferable. Examples of the azo pigment include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigment, perylene pigment, perinone pigment, anthraquinone pigment, quinacridone pigment, dioxazine pigment, indigo pigment, thioindigo pigment, isoindolinone pigment, and quinophthalone pigment. Examples of the dye chelate include a basic dye type chelate and an acid dye type chelate.

Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black.

Specific examples of the pigment that can be used in the present invention include the pigments described in paragraphs 0142 to 0145 of JP-A-2007-100071.

The volume average particle size of the pigment in the aqueous ink composition of the present invention is preferably 10 to 200 nm, more preferably 10 to 150 nm, and even more preferably 10 to 100 nm. When the volume average particle size is 200 nm or less, the color reproducibility is improved, and in the case of the inkjet method, the drip characteristics are improved. Further, when the volume average particle diameter is 10 nm or more, the light resistance becomes good. The volume average particle diameter of the pigment in the aqueous ink composition can be measured by a known measuring method. Specifically, it can be measured by a centrifugal sedimentation light transmission method, an X-ray transmission method, a laser diffraction / scattering method, or a dynamic light scattering method.
Further, the particle size distribution of the pigment in the aqueous ink composition of the present invention is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Further, two or more kinds of colorants having a monodisperse particle size distribution may be mixed and used.
The volume average particle size of the pigment can be measured by the same method as the above-mentioned measurement of the volume average particle size of the resin fine particles.

When the water-based ink composition of the present invention contains a pigment, the content of the pigment in the water-based ink composition is preferably 1 to 20% by mass, more preferably 1 to 10% by mass, from the viewpoint of colorability and storage stability. preferable.

− Dispersant −
When the water-based ink composition of the present invention contains a pigment, as the pigment, colored particles in which the pigment is dispersed in an aqueous medium by a dispersant (hereinafter, simply referred to as “colored particles”) are prepared, and this is used as the water-based ink composition. It is preferable to use it as a raw material for goods.
The dispersant may be a polymer dispersant or a low molecular weight surfactant type dispersant. Further, the polymer dispersant may be either a water-soluble polymer dispersant or a water-insoluble polymer dispersant.

As the low-molecular-weight surfactant-type dispersant, for example, the known low-molecular-weight surfactant-type dispersants described in paragraphs 0047 to 0052 of JP-A-2011-178029 can be used.

Among the above polymer dispersants, examples of the water-soluble dispersant include hydrophilic polymer compounds. For example, natural hydrophilic polymer compounds include vegetable polymers such as arabic gum, tragan gum, guar gum, karaya gum, locust bean gum, arabinogalactone, pectin, and quince seed starch, and seaweed highs such as alginic acid, carrageenan, and agar. Examples include molecules, animal macromolecules such as gelatin, casein, albumin and collagen, and microbial macromolecules such as xantene gum and dextran.

In addition, as hydrophilic polymer compounds modified from natural products, fibrous polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose, starch such as sodium starch glycolate and sodium starch phosphate ester. Examples thereof include based polymers, seaweed polymers such as sodium alginate and propylene glycol alginate.
Further, as the synthetic hydrophilic polymer compound, vinyl alcohols such as polyvinyl alcohol, polyvinylpyrrolidone and polyvinylmethyl ether, non-crosslinked polyacrylamide, polyacrylic acid or its alkali metal salt, water-soluble styrene acrylic resin and the like can be used. Acrylic resin, water-soluble styrene maleic acid resin, water-soluble vinyl naphthalene acrylic resin, water-soluble vinyl naphthalene maleic acid resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salt of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium, amino Examples thereof include polymer compounds having a salt of a cationic functional group such as a group in the side chain, and natural polymer compounds such as cellac.

Among these, a hydrophilic polymer compound having a carboxy group introduced, such as a homopolymer of acrylic acid or methacrylic acid, a copolymer of acrylic acid or methacrylic acid and another monomer, is preferable.

The water-insoluble polymer dispersant is a water-insoluble polymer, and is not particularly limited as long as the pigment can be dispersed, and conventionally known water-insoluble polymer dispersants can be used. The water-insoluble polymer dispersant can be composed, for example, containing both hydrophobic structural units and hydrophilic structural units.

Here, examples of the monomer component constituting the hydrophobic structural unit include a styrene-based monomer component, an alkyl (meth) acrylate component, an aromatic group-containing (meth) acrylate component, and the like.
Further, the monomer component constituting the hydrophilic structural unit is not particularly limited as long as it is a monomer component containing a hydrophilic group. Examples of this hydrophilic group include a nonionic group, a carboxy group, a sulfonic acid group, a phosphoric acid group and the like. Examples of the nonionic group include a hydroxyl group, an amide group (without substitution of a nitrogen atom), a group derived from an alkylene oxide polymer (for example, polyethylene oxide, polypropylene oxide, etc.), a group derived from a sugar alcohol, and the like.
From the viewpoint of dispersion stability, the hydrophilic structural unit preferably contains at least a carboxy group, and it is also preferable that the hydrophilic structural unit contains both a nonionic group and a carboxy group.

Specific examples of the water-insoluble polymer dispersant include styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, and (meth) acrylic acid ester- (meth). ) Acrylic acid copolymer, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, styrene-maleic acid copolymer and the like can be mentioned.

The water-insoluble polymer dispersant is preferably a vinyl polymer containing a carboxy group from the viewpoint of dispersion stability of the pigment. Further, a vinyl polymer having at least a structural unit derived from an aromatic group-containing monomer as a hydrophobic structural unit and a structural unit containing a carboxy group as a hydrophilic structural unit is more preferable.

The weight average molecular weight of the water-insoluble polymer dispersant is preferably 3,000 to 200,000, more preferably 5,000 to 100,000, still more preferably 5,000 to 5,000, from the viewpoint of dispersion stability of the pigment. It is 80,000, particularly preferably 10,000 to 60,000.

From the viewpoint of pigment dispersibility, ink colorability, and dispersion stability, the content of the dispersant in the colored particles is preferably 10 to 90 parts by mass with respect to 100 parts by mass of the pigment, and is preferably 20 to 70 parts by mass. By mass is more preferred, and 30 to 50 parts by mass is particularly preferred.
When the content of the dispersant in the colored particles is within the above range, the pigment is coated with an appropriate amount of the dispersant, and the colored particles having a small particle size and excellent stability over time tend to be easily obtained, which is preferable.

The colored particles can be obtained by dispersing a mixture containing, for example, a pigment, a dispersant, and if necessary, a solvent (preferably an organic solvent) with a disperser.
More specifically, for example, after a step (mixing / hydration step) of adding an aqueous solution containing a basic substance to a mixture of a pigment, a dispersant, and an organic solvent that dissolves or disperses the dispersant, the organic solvent It can be produced as a dispersion by providing a step (solvent removing step) excluding. As a result, the pigment is finely dispersed, and a dispersion of colored particles having excellent storage stability can be produced.

The organic solvent needs to be able to dissolve or disperse the dispersant, but in addition, it preferably has a certain affinity for water. Specifically, those having a solubility in water at 20 ° C. of 10 to 50% by mass or less are preferable.
Preferred examples of the organic solvent include a water-soluble organic solvent. Of these, isopropyl alcohol, acetone and methyl ethyl ketone are preferable, and methyl ethyl ketone is particularly preferable. The organic solvent may be used alone or in combination of two or more.

The basic substance is used for neutralizing an anionic group (preferably a carboxy group) that the polymer may have. The degree of neutralization of the anionic group is not particularly limited. Usually, it is preferable that the final dispersion of the colorant particles has a liquid property of, for example, a pH of 4.5 to 10. The pH can also be determined by the desired degree of neutralization of the polymer.

The method for removing the organic solvent in the production process of the colored particle dispersion is not particularly limited, and the organic solvent can be removed by a known method such as vacuum distillation.

In the water-based ink composition of the present invention, the colored particles may be used alone or in combination of two or more.

<Surfactant>
The water-based ink composition of the present invention may contain a surfactant as a surface tension adjusting agent.
As the surfactant, any of an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, and a betaine-based surfactant can be used.

Specific examples of anionic surfactants include sodium dodecylbenzene sulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalene sulfonate, sodium dialkyl sulfosuccinate, sodium stearate, potassium oleate, and sodium dioctyl. Sodium sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkylate sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium dialkyl sulfosuccinate, sodium oleate, sodium t-octylphenoxyethoxypolyethoxyethyl sulfate, etc. , And one or more of these can be selected.

Specific examples of the nonionic surfactant include acetylene diol derivatives such as ethylene oxide adducts of acetylene diol, polyoxyethylene lauryl ether, polyoxyethylene octylphenyl ether, polyoxyethylene oleylphenyl ether, and polyoxyethylene nonyl. Examples thereof include phenyl ether, oxyethylene / oxypropylene block copolymer, t-octylphenoxyethyl polyethoxyethanol, nonylphenoxyethyl polyethoxyethanol and the like, and one or more of these can be selected.

Examples of the cationic surfactant include tetraalkylammonium salt, alkylamine salt, benzalkonium salt, alkylpyridium salt, imidazolium salt and the like, and specific examples thereof include dihydroxyethylstearylamine and 2-heptadecenyl. -Hydroxyethyl imidazoline, lauryldimethylbenzylammonium chloride, cetylpyridinium chloride, stearamide methylpyridium chloride and the like.
Among these surfactants, nonionic surfactants are preferable, and acetylene diol derivatives are more preferable, from the viewpoint of stability.

The content of the surfactant in the water-based ink composition is preferably an amount that can keep the water-based ink composition within the range of the following surface tension. More specifically, the content of the surfactant in the water-based ink composition is preferably 0.1% by mass or more, more preferably 0.1 to 10% by mass, and further preferably 0.2. ~ 3% by mass.

<Other ingredients>
The water-based ink composition of the present invention further comprises a drying inhibitor (swelling agent), a coloring inhibitor, a penetration accelerator, an ultraviolet absorber, a preservative, a rust inhibitor, a defoaming agent, a clay regulator, as required. Additives such as pH adjusters and chelating agents may be mixed. The mixing method is not particularly limited, and a commonly used mixing method can be appropriately selected to obtain the aqueous ink composition of the present invention.

<Physical characteristics of water-based ink composition>
The viscosity of the aqueous ink composition of the present invention at 30 ° C. is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more and less than 13 mPa · s, and further preferably. It is 2.5 mPa · s or more and less than 10 mPa · s.
The viscosity of the aqueous ink composition is measured using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) at a temperature of 30 ° C.

From the viewpoint of dispersion stability, the pH of the aqueous ink composition of the present invention is preferably 6 to 11 at 25 ° C., more preferably 7.0 to 10.0, and 7.0 to 9.0. Is more preferable. The pH of the ink is measured using a pH meter WM-50EG (manufactured by Toa DDK Co., Ltd.) in an environment of 25 ° C.

When the water-based ink composition of the present invention is used in an inkjet recording method, it is preferable to adjust the amount of the surfactant so that the surface tension of the water-based ink composition is 20 to 60 mN / m from the viewpoint of ink ejection property. The amount is more preferably 20 to 45 mN / m, and even more preferably 25 to 40 mN / m.
The surface tension of the water-based ink composition is measured at a temperature of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[Image formation method]
The image forming method of the present invention includes an ink applying step of applying the aqueous ink composition of the present invention onto a recording medium by an inkjet method to form an image.
Further, the image forming method of the present invention is a step of drying and removing water and an organic solvent in the water-based ink composition applied to the recording medium (hereinafter, also referred to as “ink drying step”) and water-based, if necessary. Other steps such as a step of melt-fixing the resin fine particles contained in the ink composition (hereinafter, also referred to as “heat fixing step”) may be further included.
The ink application step is preferably a step of directly applying the water-based ink composition of the present invention onto a low water absorption recording medium or a non-water absorption recording medium to form an image.
Directly applying ink onto a low-water absorption recording medium or non-water-absorbent recording medium means that the applied ink is in direct contact with the low-water absorption recording medium or non-water-absorbent recording medium. For example, when a treatment liquid known in the field of an image forming method using a water-based ink composition is applied in advance for the purpose of agglutinating components such as resin fine particles contained in the water-based ink composition, the water-based ink composition And the low water absorption recording medium or the non-water absorption recording medium do not come into direct contact with each other. Examples of the above-mentioned known treatment liquid include the treatment liquid described in JP-A-2012-40778.
Further, in the image forming method of the present invention, it is preferable not to apply the above-mentioned known treatment liquid after the ink application step. That is, it is preferable that the image forming method of the present invention does not include the step of applying the above-mentioned known treatment liquid.

In the conventional inkjet method using an aqueous ink composition, particularly when a low water absorption recording medium or a non-water absorption recording medium is used as the recording medium, for example, a precoat liquid or a top coat liquid is used on the recording medium. There is known a method of aggregating the components in the water-based ink composition ejected into the water-based ink composition to suppress the spread of the water-based ink composition and improve the image quality.
However, since the water-based ink composition of the present invention exhibits the above-mentioned excellent properties and can impart high performance to an image, a low water absorption recording medium or non-water absorption recording medium or non-water absorption can be obtained without using a precoat liquid or a topcoat liquid. An image with excellent image quality can be formed on a sex recording medium.

<Recording medium>
The recording medium used in the image forming method of the present invention is not particularly limited, but a paper medium is preferable. That is, general printing paper mainly composed of cellulose such as so-called high-quality paper, coated paper, and art paper, which is used for general offset printing and the like, can be used.

As the recording medium, commercially available ones can be used, for example, "OK Prince High Quality" manufactured by Oji Paper Industries, "Shiraoi" manufactured by Nippon Paper Industries, and "New NPI" manufactured by Nippon Paper Industries. High-quality paper (A) such as "High-quality", high-quality coated paper such as "Silver Diamond" manufactured by Nippon Paper Industries, "OK Everlight Coat" manufactured by Oji Paper Industries, and "Aurora S" manufactured by Nippon Paper Industries. Lightweight coated paper (A3) such as Kougami, "OK Coated L" manufactured by Oji Paper Industries and "Aurora L" manufactured by Nippon Paper Industries, "OK Top Coat +" manufactured by Oji Paper Industries, and "OK Top Coat +" manufactured by Nippon Paper Industries. Coated papers such as "Aurora Coat" and "Eurite" (A2, B2), "OK Kanto +" manufactured by Oji Paper Industries, and art papers (A1) such as "Tokuryo Art" manufactured by Mitsubishi Paper Industries, etc. can be mentioned. .. It is also possible to use various photographic papers for inkjet recording.

Among the recording media, so-called coated paper (coated paper) used for general offset printing and the like is preferable. The coated paper is formed by applying a coating material to the surface of high-quality paper, acid-free paper, etc., which is mainly composed of cellulose and is generally not surface-treated, to provide a coating layer. Coated paper tends to cause quality problems such as image gloss and abrasion resistance in image formation by ordinary water-based inkjet, but gloss unevenness is suppressed when the water-based ink composition of the present invention is used. It is possible to obtain an image having good glossiness and scratch resistance. In particular, it is preferable to use a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate. Art paper, coated paper, lightweight coated paper or lightly coated paper is more preferable.

Among the above, a low water absorption recording medium or a non-water absorption recording medium should be used as the recording medium from the viewpoint of obtaining a high-quality image having a large effect of suppressing pigment movement and having a better color density and hue than before. Is preferable. In the present invention, the low water absorption recording medium means a medium having a water absorption coefficient Ka of 0.05 to 0.5 mL / m ² · ms ^1/2 , and is 0.1 to 0.4 mL / m ² ·. it is preferably ms ^1/2, and more preferably 0.2~0.3mL ^/ m 2 ^{· ms 1/2.} The non-water-absorbent recording medium means a medium having a water absorption coefficient Ka of less than 0.05 mL / m ² · ms ^1/2 .
The water absorption coefficient Ka is synonymous with that described in JAPAN TAPPI Pulp and Paper Test Method No. 51: 2000 (Published by the Pulp and Paper Technology Association). Specifically, the absorption coefficient Ka is an automatic scanning liquid absorption meter. It is calculated from the difference in the amount of water transfer between the contact time of 100 ms and the contact time of 900 ms using KM500Win (manufactured by Kumagai Riki Co., Ltd.).

<Ink application process>
In the ink applying step, the aqueous ink composition of the present invention containing a pigment is applied onto a recording medium. The method for applying the water-based ink composition is not particularly limited as long as it is an inkjet method capable of applying the water-based ink composition on an image, and a known ink applying method can be used. The inkjet method has advantages such as a compact recording device and high-speed recording performance.
In image formation by an inkjet method (method), an aqueous ink composition is ejected onto a recording medium by supplying energy to form a colored image. As a preferable inkjet recording method for the present invention, the method described in paragraphs 093 to 0105 of JP-A-2003-306623 can be applied.

The inkjet method is not particularly limited, and is known, for example, a charge control method for ejecting ink by using an electrostatic attraction, a drop-on-demand method (pressure pulse method) which uses the vibration pressure of a piezo element, and the like. Either an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink to eject the ink using radiation pressure, or a thermal inkjet method that heats the ink to form bubbles and uses the generated pressure. You may.
Further, the inkjet head used in the inkjet method may be an on-demand method or a continuous method. Further, the ink nozzle or the like used when recording by the above-mentioned inkjet method is not particularly limited, and can be appropriately selected depending on the purpose.
The inkjet method includes a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality by using multiple inks having substantially the same hue but different densities, and colorless and transparent inks. The method to be used is included.

In addition, as an inkjet method, a shuttle method that uses a short serial head and scans the head in the width direction of the recording medium for recording, and a line head in which recording elements are arranged corresponding to the entire area of one side of the recording medium. There is a line method using. In the line method, the image can be recorded on the entire surface of the recording medium by scanning the recording medium in the direction orthogonal to the arrangement direction of the recording elements, and a transport system such as a carriage that scans the short head becomes unnecessary. Further, since the movement of the carriage and the complicated scanning control between the recording medium and the recording medium are not required and only the recording medium is moved, the recording speed can be increased as compared with the shuttle method.

When the ink application step is carried out by an inkjet method, the amount of droplets of the aqueous ink composition ejected by the inkjet method is preferably 1.5 to 10 pL from the viewpoint of forming a high-definition print, preferably 1.5 to 10 pL. It is more preferable that it is 6 pL. The amount of droplets of the water-based ink composition to be ejected can be adjusted by appropriately adjusting the ejection conditions.

<Ink drying process>
The image forming method of the present invention includes an ink drying step of drying and removing an aqueous medium (for example, water, the above-mentioned water-soluble organic solvent, etc.) in the aqueous ink composition applied onto the recording medium, if necessary. You may be. The ink drying step is not particularly limited as long as at least a part of the aqueous medium in the aqueous ink composition can be removed, and a commonly used method can be applied.

<Heat fixing process>
If necessary, the image forming method of the present invention preferably includes a heat fixing step after the ink drying step. By performing the heat fixing treatment, the image on the recording medium is fixed, and the resistance to scratching of the image can be further improved. As the heat fixing step, for example, the heat fixing step described in paragraphs 0112 to 0120 of JP-A-2010-22415 can be adopted.

<Ink removal process>
The image forming method of the present invention may include, if necessary, an ink removing step of removing the water-based ink composition (for example, the solid ink solidified by drying) adhering to the head for inkjet recording with a maintenance liquid. Good. As for the details of the maintenance liquid and ink removing step, the maintenance liquid and ink removing step described in International Publication No. 2013/180074 can be preferably applied.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. Unless otherwise specified, "parts" and "%" representing the composition are based on mass.

[Synthesis of resin fine particles]
Below, the resin fine particles C-1 to C-11 and CR-1 to CR-5 used in Examples and Comparative Examples were synthesized as follows.

<Synthesis of resin fine particles C-1 and preparation of aqueous dispersion of resin fine particles C-1>
Water (342 g), Neoperex G-15 (16 mass% sodium dodecylbenzene sulfonate aqueous solution, manufactured by Kao Chemical Co., Ltd.) (9) in a three-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas introduction tube. .6 g) was charged and the temperature was raised to 85 ° C. by nitrogen air flow. A mixed solution consisting of sodium persulfate (radical polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd.) (0.07 g) and water (20 g) was added thereto, and the mixture was stirred for 10 minutes. Next, in the three-necked flask, styrene (monomer leading to the following structural unit c2-1) (60 g), 2-ethylhexyl methacrylate (monomer leading to the following structural unit c3-2) (40 g), methyl methacrylate (the following structural unit c3-). 1 (monomer leading to 1) (80 g), Eleminor JS-10 (manufactured by Sanyo Kasei Co., Ltd., 38% by mass aqueous solution, monomer leading to the following structural unit c1-1) (52.6 g) and water (167.4 g) are stirred. The obtained suspension was added dropwise with a dropping pump at a constant velocity so that the dropping was completed in 3 hours while continuing to stir, and at the same timing, sodium persulfate (0.52 g) and water were added from another pump. The mixed solution consisting of (30 g) was added dropwise at a constant velocity so that the dropping was completed in 3 hours, and the mixture was stirred for 1 hour after the dropping was completed. A 1N aqueous sodium hydroxide solution was added to the obtained reaction mixture until the pH was between 8 and 9, and the mixture was filtered through a mesh having a mesh of 50 μm to obtain an aqueous dispersion of resin fine particles C-1.

The obtained aqueous dispersion of the resin fine particles C-1 had a pH of 8.4 and a solid content concentration of 26%. The solid content concentration refers to the total amount of other components in the aqueous dispersion excluding the solvent (water and organic solvent).
The resin fine particles C-1 in the aqueous dispersion had a volume average particle size of 47 nm (the volume average particle size was measured with Microtrack UPA EX-150 (manufactured by Nikki So Co., Ltd.)) and a weight average molecular weight (according to the above measurement method). It was 120,000.

<Preparation of aqueous dispersions of resin fine particles C-2 to C-11 and CR-1 to CR-4>
In the preparation of the aqueous dispersion of the resin fine particles C-1, the preparation of the aqueous dispersion of the resin fine particles C-1 except that the type and amount of the monomer used were changed to the types and composition ratios of the monomers shown in Table 1. In the same manner, aqueous dispersions of resin fine particles C-2 to C-11 and CR-1 to CR-4 were prepared, respectively.
<Synthesis of resin fine particles CR-5 and preparation of aqueous dispersion>
A resin fine particle CR-5 was synthesized and a dispersion thereof was prepared according to the method described in Japanese Patent Application No. 2015-072387.
In the resin fine particles C-2 to C-11 and CR-1 to CR-5, when M was a potassium cation or an ammonium cation, M was converted to a potassium cation or an ammonium cation by a conventional method using a potassium salt or ammonia. ..
Table 1 shows the physical characteristics of the obtained resin fine particles C-2 to C-11 and CR-1 to CR-5, and their aqueous dispersion.

Specific examples of the structural units constituting each resin fine particle are shown below.
The "*" shown in the following structural units indicates the connection site with other structural units.

In the "Structural unit" column of Table 1, "-" indicates that it does not have a corresponding structural unit. Further, in the "composition ratio" column, the blank indicates that the content is 0% by mass.

[Example 1]
<Preparation of water-based ink composition>
(Preparation of Black Ink Compositions K-1 to K-11 and CK-1 to CK-11)
-Synthesis of water-soluble polymer dispersant Q-1-
A monomer feed composition was prepared by mixing methacrylic acid (172 parts), benzyl methacrylate (828 parts), and isopropanol (375 parts). In addition, an initiator feed composition was prepared by mixing 2,2-azobis (2-methylbutyronitrile) (22.05 parts) and isopropanol (187.5 parts).
Next, isopropanol (187.5 parts) was heated to 80 ° C. under a nitrogen atmosphere, and a mixture of the monomer supply composition and the initiator supply composition was added dropwise thereto over 2 hours. After completion of the dropping, the obtained solution was kept at 80 ° C. for another 4 hours and then cooled to 25 ° C.
After cooling, the solvent was removed under reduced pressure to obtain a water-soluble polymer dispersant Q-1 having a weight average molecular weight of about 30,000 and an acid value of 112 mgKOH / g.

-Preparation of black pigment dispersion-
After neutralizing 0.8 equivalents of the amount of methacrylic acid in the water-soluble polymer dispersant Q-1 (150 parts) obtained above with an aqueous potassium hydroxide solution, the concentration of the water-soluble polymer dispersant was 25 mass by mass. The concentration was adjusted by further adding ion-exchanged water to obtain an aqueous solution of a water-soluble polymer dispersant.
This water-soluble polymer dispersant aqueous solution (124 parts), carbon black MA-100 (black pigment, average particle size 80 nm) (48 parts), water (75 parts), and dipropylene glycol (30 parts) are mixed. Then, the mixture was dispersed in a bead mill (bead diameter 0.1 mmφ, zirconia beads) until a desired volume average particle size was obtained to obtain a dispersion (uncrosslinked dispersion) of polymer-coated black pigment particles having a pigment concentration of 15%.
To this uncrosslinked dispersion (136 parts), a crosslinking agent: Denacol EX-321 (manufactured by Nagase ChemteX Corporation) (1.3 parts) and an aqueous boric acid solution (boric acid concentration: 4% by mass) (14.3 parts). ) Was added, and the mixture was reacted at 50 ° C. for 6 and a half hours and then cooled to 25 ° C. to obtain a crosslinked dispersion. Next, ion-exchanged water was added to the obtained crosslinked dispersion, and ultrafiltration was performed using a stirring type ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (manufactured by ADVANTEC, molecular weight cut-off 50,000, Q0500076E ultrafilter). Filtration was performed. A black pigment dispersion was obtained by purifying the crosslinked dispersion so that the concentration of dipropylene glycol was 0.1% by mass or less and then concentrating until the pigment concentration was 15% by mass. The pigment contained in the black pigment dispersion is a polymer-coated pigment (encapsulating pigment) whose surface is coated with a crosslinked polymer in which the water-soluble polymer dispersant Q-1 is crosslinked with a crosslinking agent.

-Preparation of black ink compositions K-1 to K-11 and CK-1 to CK-11-
Each component was mixed so as to have the following composition, and an ink composition containing each resin fine particle was prepared. After the liquid preparation, coarse particles were removed using a 1 μm filter to prepare black ink compositions K-1 to K-11 and CK-1 to CK-11, respectively.
〔composition〕
Black pigment dispersion: Amount at which the concentration of the black pigment is 4 parts by mass Hydrophobic organic solvent (d1) shown in Table 2: Content shown in Table 2 Organic solvent (dr1) shown in Table 2: Content shown in Table 2. Aqueous dispersion of resin fine particles shown in Table 2: Content shown in Table 2 (converted to resin fine particle content)
Surfactant Capstone FS-3100 (manufactured by DuPont): 0.1 parts by mass Water: Remaining total: 100 parts by mass

The viscosities of the black ink compositions prepared above were all in the range of 3 to 15 mPa · s at 30 ° C. This viscosity was measured on VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).
The surface tension was measured by the platinum plate method using CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. The surface tensions of the black ink compositions prepared above were all in the range of 20 to 60 mN / m.

[Test example]
The following tests were performed on each black ink composition prepared as described above (hereinafter, may be simply referred to as "ink"). The results are shown in Table 2 below.

(Image formation)
Image formation in the following test was performed as follows.
Coated paper (trade name "OK Top Coat +", manufactured by Oji Paper Co., Ltd.) was used as the base material, and the inks K-1 to K-11 and CK-1 to CK-11 were prepared by a single pass method, respectively. An image was formed by discharging under the following conditions.
<Conditions>
・ Head: 1,200 dpi (dot per inch, 1 inch = 2.54 cm) / 20 inch width piezo full line head ・ Discharge amount: 2.4 pL
-Drive frequency: 30 kHz (base material transfer speed 635 mm / sec)

<Test 1: Evaluation of dischargeability>
After forming a solid image with a recording duty of 100% on one recording medium according to the above (image forming) method, the printing machine is stopped for 30 minutes under the conditions of 25 ° C. and 50% relative humidity, and the print head is moved to the atmosphere. Exposed. After stopping for 30 minutes, a nozzle check pattern of the inkjet recording device was formed on one recording medium according to the above (image formation) method. The formed nozzle check pattern was visually observed, and the number of ejection failure nozzles (unit: number) was counted. It was determined which of the following evaluation criteria the number of ejection failure nozzles was included in.
In this test, if the number of ejection failure nozzles is 2 or less, it is within the practically permissible range. The evaluation results are shown in Table 2.
The recording duty of 100% is defined as an image recorded under the condition that one drop of about 2.4 pL of ink is applied to a unit area (1 pixel) of 1/1200 inch × 1/1200 inch with a resolution of 1200 dpi × 1200 dpi.
− Evaluation criteria −
AA: 0 A: 1-2 B: 3-5 C: 6 or more

<Test 2: Evaluation of storage stability>
Each ink was packed in a closed container made of Teflon (registered trademark) and left in a constant temperature room at 60 ° C. for 4 weeks for a storage test. The viscosity of the ink before and after the storage test was measured, and the rate of change in the viscosity of the ink was calculated from the following formula. The viscosity of the ink was measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) at a temperature of 30 ° C.
It was determined which of the following evaluation criteria included the obtained viscosity change rate. The closer the rate of change in the viscosity of the ink is to 1.0, the higher the storage stability of the ink. In this test, if the viscosity change rate is less than 1.2, it is within the practically acceptable range. The evaluation results are shown in Table 2.

Viscosity change rate = (viscosity of ink after storage test) / (viscosity of ink before storage test)

− Evaluation criteria −
A: less than 1.1 B: 1.1 or more and less than 1.2 C: 1.2 or more

<Test 3: Evaluation of abrasion resistance>
A solid image having a recording duty of 100% was formed on the recording medium according to the above (image forming) method, and then left in an environment of 25 ° C. for 24 hours and a relative humidity of 50%. The image forming surface of this recording medium was scraped 50 times with Sylphon paper loaded with a load of 2 × 10 ⁴ N / m ² . Then, the surface condition of the image-forming portion (solid image) was visually confirmed. It was determined which of the following evaluation criteria the surface condition corresponds to.
In this test, if it is equal to or higher than the following evaluation standard B, it is within the practically acceptable range. The evaluation results are shown in Table 2.
− Evaluation criteria −
A: There were no scratches on the image.
B: The image had slight scratches.
C: The image had scratches, and the white background (surface) of the recording medium was visible.

<Test 4: Evaluation of dryness>
A solid image with a recording duty of 100% was formed on one recording medium according to the above (image formation) method. The obtained print is rubbed by hand under the conditions of 25 ° C. and 50% relative humidity after 10 seconds, 20 seconds, and 30 seconds, respectively, and the quick-drying fixability of the ink is confirmed and dried. It was used as an index for sexual evaluation. It was determined which of the following evaluation criteria this index corresponds to.
In this test, if it is equal to or higher than the following evaluation standard B, it is within the practically acceptable range. The evaluation results are shown in Table 2.
− Evaluation criteria −
AA: Even if the solid print portion is touched 10 seconds after printing, the printed surface does not peel off.
A: If the solid print portion is touched 10 seconds after printing, the printed surface peels off, but even if the solid printed portion is touched 20 seconds after printing, the printed surface does not peel off.
B: If the solid printed portion is touched 20 seconds after printing, the printed surface peels off, but if it is touched 30 seconds after printing, the printed surface does not peel off.
C: If the solid print portion is touched 30 seconds after printing, the printed surface peels off.

<Test 5: Evaluation of image quality>
An image with a recording duty of 80% was recorded on one recording medium according to the above (image formation) method, and the graininess (presence or absence of graininess) of the obtained printed matter was visually confirmed and used as an index of image quality. .. It was determined which of the following evaluation criteria this index corresponds to.
In this test, if it is equal to or higher than the following evaluation standard B, it is within the practically acceptable range. The evaluation results are shown in Table 2.
− Evaluation criteria −
A: There is no graininess.
B: A slight graininess is observed.
C: A remarkable graininess is observed.

<Test 6: Evaluation of filterability>
Each of the prepared black ink compositions was circulated for 45 hours using a pump at a flow velocity of 6 mL / min through a polypropylene filter (mesh 3 μm, cross-sectional area 5 cm ² ) installed at one location in the middle of the circulation path. In each black ink composition, the resin fine particles were finely dispersed (for example, about 80 nm). The amount of pressure increase after 45-hour circulation (pressure after 45-hour circulation-pressure before circulation) was determined with respect to the pressure before circulation. It was determined which of the following evaluation criteria the pressure increase amount was included in. This pressure increase occurs when the resin fine particles in the ink composition reaggregate or gel during filtration (during production) of the ink composition, thereby clogging the filter.
In this test, when the amount of pressure increase is less than 40 kPa, the resin fine particles in the ink are suppressed from reaggregating or gelling during the production of the ink composition, and the filter by these reaggregates or gelled products is suppressed. It is possible to suppress clogging of the ink, which is within the practically acceptable range. The evaluation results are shown in Table 2.
− Evaluation criteria −
A: Less than 5 kPa B: 5 kPa or more and less than 40 kPa C: 40 kPa or more

<Notes in Table 2>
In Table 2, * organic solvents (dr1-1) and (dr1-2) should be listed in the organic solvent (dr) column, but in order to make it easier to compare the ClogP values, the hydrophobic organic solvent (d1) ) Is described in the column.
In Table 2, PG indicates propylene glycol (ClogP value: -1.06), and DPG indicates dipropylene glycol (ClogP value: -0.69).

As shown in Table 2, the aqueous ink compositions for inkjet recording (CK-1 to CK-11) of Comparative Examples and Reference Examples in which the resin fine particles specified in the present invention and the hydrophobic organic solvent are not used in combination are used. None of them have storage stability, filterability, ejection property, drying property, image quality and abrasion resistance.
In particular, even if the resin fine particles specified in the present invention are contained, a water-soluble organic solvent such as glycerin, (di) ethylene glycol or ethanol is used in combination, and the hydrophobic organic solvent specified in the present invention is not contained, or the present invention. The aqueous ink composition for inkjet recording (CK-1 to CK-5) of the comparative example which does not satisfy the content specified in the invention is inferior in dryness or image quality, and in some cases, inferior in filterability. On the other hand, the aqueous ink compositions for inkjet recording (CK-6 to CK-9) of Comparative Examples containing the hydrophobic organic solvent specified in the present invention but not containing the resin fine particles specified in the present invention At least, it is inferior in dischargeability. The water-based ink composition for inkjet recording (CK-11) of the comparative example which does not contain resin fine particles does not show sufficient performance in moisture resistance and image quality.

On the other hand, all of the aqueous ink compositions for inkjet recording (K-1 to K-11) of the examples containing the resin fine particles specified in the present invention in combination with the hydrophobic organic solvent (d1) are all. It shows high storage stability and filterability. Moreover, when applied to an inkjet recording method, it is possible to form an image having excellent ejection properties and drying properties, and further excellent image quality and abrasion resistance.

Moreover, when the cyan ink composition and the magenta ink composition prepared by using the cyan pigment and the magenta pigment were tested in the same manner as the above black ink composition, the same results were shown.

Claims (8)

An aqueous ink composition for inkjet recording containing water, an organic solvent, and resin fine particles.
The organic solvent contains an alcohol solvent as a hydrophobic organic solvent (d1) having a ClogP value of 0 to 3.5 and an organic solvent (dr1) having a ClogP value of −3.0 or more and less than 0 .
The content of the hydrophobic organic solvent (d1) in the aqueous ink composition for inkjet recording is 0.5 to 10% by mass, and the total of the hydrophobic organic solvent (d1) and the organic solvent (dr1). The content is 6-40% by mass,
The resin fine particles have a structural unit represented by the following general formula (I) in the resin fine particles in an amount of 3 to 20% by mass , and the structural unit represented by any of the following general formulas (A) to (E). A water-based ink composition for inkjet recording.

In the general formula (I), R represents an alkylene group having 7 to 30 carbon atoms. L ¹ represents a single bond , **-alkylene group-C (= O) -O- group or **-arylene group-C (= O) -O- group. Here, ** indicates a connection portion with the carbonyl carbon atom in the general formula (I) . R and L ¹ may have a cycloalkyl, an aromatic hydrocarbon ring group, an aromatic heterocyclic group, SO ₃ M or COOM as a substituent . L ² indicates a single bond. L ³ is shows the hydrogen atom, SO ₃ M or COOM. M represents an alkali metal ion or an ammonium ion. However, at least one of R, L ¹ and L ³ has SO ₃ M or COOM.

In the general formulas (A) to (E), R ¹¹ and R ¹² represent a methyl or hydrogen atom. R ¹³ represents a linear or branched alkyl group having 1 to 10 carbon atoms. N in the general formula (A) and the general formula (B) is an integer of 0 to 5, and n in the general formula (C) is an integer of 0 to 11. L ¹¹ is a single bond, a linear, branched or cyclic alkylene group having 1 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, -O-, -NH-, -S- or -C (=). O)-or a divalent linking group formed by linking two or more of these. The water-based ink composition for inkjet recording according to claim 1 , wherein the content of the structural unit represented by the general formula (A) in the resin fine particles is 5 to 50% by mass. The water-based ink composition for inkjet recording according to claim 1 or 2 , wherein at least one of R, L ¹ and L ³ of the general formula (I) has SO ₃ M. The aqueous ink composition for inkjet recording according to any one of claims 1 to 3, wherein the organic solvent (dr1) contains diethylene glycol, dipropylene glycol, propylene glycol or 1,2-butanediol. The inkjet recording according to any one of claims 1 to 4, wherein the content ratio (mass basis) of the hydrophobic organic solvent (d1) to the organic solvent (dr1) is 1: 1 to 1:30. Aqueous ink composition. The water-based ink composition for inkjet recording according to any one of claims 1 to 5, which contains a pigment. An image forming method including an ink applying step of applying the water-based ink composition for inkjet recording according to claim 6 onto a recording medium by an inkjet method to form an image. The image forming method according to claim 7, wherein the water-based ink composition for inkjet recording is directly applied onto a low-water-absorbing recording medium or a non-water-absorbent recording medium.